It’s October in Portland and my Agave montana is in the process of flowering…I know, we’re heading toward winter, with its rain and average low down into the mid-30’s with potentially sudden damaging temperature swings from mid-November into March dropping below freezing to the low twenties, with extremes some years, generally limited to the upper teens, though historically, some areas have dropped into the single digits, those Arctic blasts from the interior….Winter temps here can be extremely unsupportive of Agave’s from ‘low desert’ and tropical regions. Combined with these cool/cold temperatures are our seasonal reduction in daylight hours and its intensity (day length and angle of incidence varies much more widely here at 45º north) and the rain, ranging from 2.5″ to 6″+ each month here Nov.- Mar., resulting in a ‘trifecta’ of negative factors which can compromise an Agave, even when in its long rosette producing stage. Any Agave here requires thoughtful siting with special consideration for drainage, exposure and aspect. For an Agave, conditions common to the maritime Pacific Northwest are generally marginal, yet I am far from alone in my attempts to grow them here. Previously, in April of 2016 I had an Agave x ‘Sharkskin’ flower, a process that spanned the summer months, taking 7 until mid-October to produce ripe seed. I was initially a little pessimistic this time about A. montana’s prospects. Why, I wonder, if plants are driven to reproduce themselves would this one be starting the process now?
Growing in its Native Biome
Agave montana is a mountain species found in the northern portion of the Sierra Madre Orientale, SMOr, a mountain range that runs from near Texas’ Big Bend National Park and the Rio Grande, south 620 miles through the Mexican states of Nuevo Leon, Tamaulipas, San Luis Potosi, Querotaro and on into Vera Cruz, separated from the Gulf of Mexico by a coastal plain. Its native range is cut off to the west by the much drier Mexican Plateau, that averages around 3,500′ elevation, home to the Chihuahuan Desert that extends into Texas, southern New Mexico and the extreme southeast of Arizona. Arid scrub lands border the western side of the mountains. Rains typically move in from the east, the Gulf, emptying much of their moisture on the coastal plain and ascending, eastern foothills, leaving the western sections drier, but still much ‘wetter’ than the western desert below. North and east of the mountains near the Rio Grande is the Tamaulipian Mattoral, a region of desert scrubland. This includes part of the lower, most northern portion of the SMOr with a few isolated, higher, ‘sky-islands’. This regions’ species composition, though ‘desert’, is different than that of the Chihuahuan featuring many leguminous shrubs and succulents, among them many endemic cacti and Agave victoriae-reginae. There are 20 or so of Mexico’s endemic Agave species in this mattoral.
South of the Tamaulipan Mattoral it becomes increasingly wet along the north-south running mountain ridges, the rainfall carrying on up as the clouds rise and cool into the mountains of the SMO. Much of the SMOr is high enough to be temperate, some of the peaks and high ridgelines even more extreme. Heading southerly through this range the region grades into tropical and subtropical cloud-forest to rain-forest with radically different plant and animal populations.
This entire region, fronting on the Gulf, shares its precipitation pattern, with consistent, but lower, accumulations during much of the year tripling or more during the hurricane season that bunches around September, a period that varies in length from year to year, before dropping quickly off going through the Fall, the overall amounts increasing moving south, very different than ours in the Pacific Northwest.
Moving west from the coastal plain, elevations rise and the climate shifts from tropical/sub-tropical to temperate humid on the eastern slopes and temperate sub-humid, covered in Pine-Oak forest and more open woodlands. The map shows the area of Pine-Oak forest in green that sits to the cooler/drier lee of this coastal wet region. These highlands tend to have calcareous soils of sedimentary origin and contain a fairly high organic content, compared to those of the lower desert and scrublands. In the far north, drier portion of the SMOr the Pine-Oak forests exist scattered in the form of ‘Sky-Islands separated by the encroaching and surrounding Chihuahuan Desert and Mattoral in a pattern repeated in southern Arizona and New Mexico, the rainfall levels hovering around just over ten inches near Big Bend to almost 60″ in the long western ‘strip’ in the southern portion of the range.
Much of the Pine-Oak regions of the mountains, especially the drier portions have an annual rainfall averaging between 15″-25″ and much cooler temperatures. This is where Agave montana is found between 6,000′-10,000′, some sources list as high as 11,500′. Freezing and snowfall are not uncommon within its elevational range. This is a rugged range with three peaks along its north-south spine higher than our Mt. Hood, Cerro San Rafael rising to 12,238′ in the far north the other two still in Nuevo Leon. The geology of the SMO is younger than our Cascades and are a result of folding and uplift creating the long rugged ridges and ravines that define it. The several hundred mile long swath of Pine-Oak biome includes the relatively common Pinus nelsonii, P. cembroides, P. pseudostrobus, P. arizonica, Quercus affinis Q. castanea among smaller more scattered populaitons of other species. Agave montana grows as an understory plant amongst mixed open forest predominantly of Quercus miquihuanensis, Pinus hartwegii and junipers together with Arbutus xalapensis, Buddleja cordata and the tall, trunk-forming Nolina hibernica. Agave gentryi, a zn6b plant, occurs scattered in a band with A. montana, though extending another 1,000′ higher. Agave scabra borders A. montana to its east climbing up from the Chihuahuan Desert, where it can dominate, through scrubland to 4,500′ or so into the lower western SMOr.
This is the region that has shaped the development of A. montana giving it some ‘street cred’ that suggest that it could be one of the best performing Agave for our region. It is more tolerant of cool/cold temperatures, some have estimated down to 5ºF, than the many low desert species, promising to be more tolerant of our annual and seasonal pattern of rainfall. Drainage and aspect must still be considered when growing this or any Agave species, but A. montana is certainly a less picky choice than the many low desert species available in the nursery trade today. It has another habit it picked up from its thousands of years in the SMOr that should help improve its success here as well…more about that later. (Check out the Encyclopedia of Succulents here!)
On Stressors, Triggers and Regulators
Agave can wait, depending on species and growing conditions, for between 6 and 30 years, sometimes longer, before they flower. Each species has its own range, each individual varying within it. Several factors are though to have some impact on how long before a plant flowers. Water is normally the most limiting element for these under native conditions. Over its life water availability strongly impacts stress and growth rate. An Agave living under regular drought stress will grow slower, of course what is normal for an Agave would stress and kill many thousands of other plants. Some have written that it may be triggered in some way by the longer cycles of precipitation, wetter and drier years grouped in a changing cycle, but I’m not sure that would hold for this one as it comes from a region that is wetter than the typical desert environment. The thinking goes that a higher survival rate of seedlings will occur in wet years, but how would they anticipate this? Others would argue no, because in nature, for many species, it is the rare individual seedling that will survive to maturity and flower successfully, trees for instance. But, if this is so, Agave must have some way of sensing these longer cycles or detecting and ‘remembering’ rainfall patterns from year to year. Most Agave have evolved in arid landscapes, which tend to receive their precipitation during the summer months, though in more northerly regions the pattern can be split, receiving some in winter, as a result of patterns in the Pacific, and the rest as monsoonal showers, with their tropical origins. The onset of rain may serve as a trigger. It is best to ‘reproduce’ like conditions as best you can. Growing as mine does in summer dry Portland, its signals may get ‘confused’ as our rains begin at summer’s end, increasing into winter, before tapering off in spring.
When grown significantly north of their natural range, its photoperiod and range of temperatures can change radically. An Agave americana bloomed this last summer, 2019, in the Chicago Garfield Park Conservatory, after nearly 60 years growing under glass, which leads one to questions about available light. Chicago is at 42º N latitude, 3º south of us, with day light hours and its intensity causing slower carbohydrate production. Moving closer toward the poles generally reduces average temperatures and available light. These are plants adapted, as mostly residents of tropical and sub-tropical latitudes, to less of a drop off in daylight moving toward the Winter solstice. Growing in the more northerly PNW an Agave, with its slower metabolism and production of carbohydrates must be limited by our less intense light and rapidly declining daylight hours in the Fall. It is not just water and rainfall patterns we must concern ourselves with.
Many flowering plant species, are triggered by photoperiod, day length to most of us. In some plants this trigger alone is very strong. Many Onions, which are also Monocots, switch their growth pattern from foliage expansion to growth of the bulb in mid to late Spring, when under ‘normal’ conditions they would have already produced adequate top growth and photosynthetic capacity. In these plants if you plant them out too late, the resultant small top growth can produce only undersized bulbs. I suspect that photoperiod plays a more minor role in Agave as day length varies less across their natural range than it does for us very close to 45ºN. But overall available solar energy throughout the year drops off as you move towards the poles, with less energy available for growth. I imagine this could lengthen the time period required for an Agave to reach maturity with adequate stores of carbohydrate.
I have yet to find a survey of the flowering of the many species of Agave and what its linked to, latitude, photoperiod, precipitation patterns, temperature, availability of pollinators, etc. The triggering of the flowering of Agave is not fully understood within their native ranges so here in the PNW and temperate North America in general, we are even more in the ‘dark’ and left with unsupported speculation.
Last year, in July, my pot grown Agave colorata, a native of the hot, low coastal desert of Sonora and Sina Loa, Mexico, began flowering, going so far as maturing most of its flowers, many of its anthers dehiscing their pollen, in October and November, the process stalling and the flowers damaged with the onset of cool and sometimes very wet weather in October and the winter that followed. No seed was produced at all even though bees were abundant, at least for the first ‘branches’ of the maturing panicle. I was initially more than a little anxious this time around for my Agave montana.
My Agave x ‘Sharkskin’ began to bloom in April of its 18th year, 2016, and successfully completed the process (see my earlier posts). Interesting to note that it is a hybrid of Agave scabra and A. victoriae-reginae, both residents of the lower elevations around the SMO and surrounding desert/mattoral. The original plant was found there where the two species overlapped. I include the pictures that follow immediately for comparison purposes. Its peduncle reaching 20′ 3″ tall, and no more than 3″ in diameter at the base, this hybrid was fragile and I guyed it in place from three fixed points. I imagine, if enough people keep growing Agave outdoors here, monitoring their conditions and keeping notes, that someone, will eventually be able to speak a lot more directly about what is actually going on.
Living organisms are not mechanical creations. They possess a certain amount of independence, autonomy, are responsive and adaptable to the stressors in their environment and, to a great degree, self-maintaining, replacing old or damaged cells or their proteins…all having limited lifespans. We should lose the mechanical metaphors we commonly utilize when we think about them and invest ourselves in better understanding exactly what it means to be alive. An organism may ‘burn’ or oxidize carbohydrates, but it doesn’t utilize the power of explosively expanding exhaust gases to push pistons to drive it as does an internal combustion engine. It does a slow, more modulated burn of its carbohydrate fuel, oxidizing it, within each cell’s mitochondria ‘grabbing on to’ the ‘freed-up’ electrons and using the stream of produced protons in a series of bio-chemical conversions, capturing their electrical charge in bonds on ATP molecules, which serve as organic batteries within virtually every living organism. In some processes there is literally a ‘flow’ of protons that drive a tiny ‘mechanism’ putting the necessary components together. Whether using carbohydrate formed immediately from photosynthesis, using those stored in a seed’s endosperm or a plant’s various tissues, this oxidation process drives the ‘charging’/formation of ATP. It’s the same process going on within my flowering Agave, but its energies have been redirected. Agave are monocarpic and are ‘prepared’ to spend their entire storehouse of carbohydrate in their singular and final flowering act. The large majority of perennial species aren’t monocarpic and are capable of turning their flowering strategies on and off as they progress from one year to the next, reading the seasonal changes and adjusting their internal process accordingly. Once an Agave begins the flowering process, however, there is no reversal of this redirection.
The Meristem Where the Action Happens!
To better understand this it is important to know how an Agave grows. Agave are members of the Asparagus family, a classification disputed by some botanists, which belong to the larger group, the monocotyledons…from here out, simply, Monocots. I wrote about the Monocots in a previous post and what distinguishes them from the larger plant group of Eudicots, or ‘true’ Dicots, which together make up the vast bulk of the existing flowering plants, the Angiosperms. I won’t go into those details here, but I want to spend some time with what distinguishes genus Agave in terms of their patterns and how they grow.
Most basically, growth is a result of the process of cell division, the increase in cell numbers and their differentiation into the many specialized cells, tissues and organs structured into particular patterns. Cell differentiation takes place at the site of the meristematic tissue, its ‘stem’ cells. Where this meristem occurs in a plant is central to how it grows. Agave and Monocots as a group do not have a cambial meristem, they cannot add secondary growth to their stems, they produce new top growth from their singular apical meristem, there are the exceptions which branch. But what is a meristem and what does it look like? Meristem consists of a zone or layer of undifferentiated cells, which actively divide forming ‘differentiated cells’, cells of a specific type that will comprise the structures and tissues of a multi-celled organism. These new cells when first formed are not complete, but will ‘fill out’ as they grow into their mature selves. This initiation of growth can only happen in the meristem. The meristem is a ‘zone’ that is continuously moving ahead of the maturing cells, the meristem cells growing then dividing in two, leaving one cell behind that differentiates into a specialized cell as it matures ‘pushing’ the meristem ahead.
The meristem is the leading or growing edge of newly forming tissues. While other tissues and organs, like leaves may grow larger over time, to a set limit, adding necessary cells, they all begin at the meristem, the leaves and flowers themselves as ‘primordia’, tiny incipient ‘models’ of their larger selves, the ‘pattern’ set. ‘Plate’ meristem borders each of these new, expanding leaves, their edges dividing much as does the apical meristem, before slowing and eventually completely disappearing once the organ’s mature size is reached. Along the way they form cells to grow the veins, mesophyll, stoma and guard cells, a leaf’s epidermis and all of the other specialized cells that comprise it.
The Apical Meristem: Doing the ‘Groundwork’
At its beginning as a seedling a tiny rosette begins to form with the emergence of a single leaf. Agave seedlings begin producing root and top growth from whatever it has stored in its remaining cotyledon or ‘seed leaf’, Monocots have only one. Once that is spent their growth is dependent upon the photosynthetic power of their leaves, storing what they can as reserves in their tissues. In Agave and many other Monocots, especially those we commonly refer to as bulbs or geophytes they store much of this ‘extra’ carbohydrate in a specialized storage organ to hold the energy rich starches they will need later. These storage organs form from modified stem tissues just ‘above’ the roots, for bulbs these are underground while in Agave they are above. As growth goes on over time an Agave’s ‘heart’ increases in girth and volume, the meristem itself expanding in cross section growing and stretching into a broader ‘disk’ or ‘cap’. Palm trees do this, Bananas do this, Orchids do this, all Monocots do this following their own specific patterns.
Newly formed leaves, arise from the center and ‘drift’ to the periphery of the meristem as it increases in size. The leaves form continuously in response to its conditions and the imperatives which drive it. Over this time its productive capacity increases with the collective surface area of its leaves growing the leaves, the ‘heart’ and meristem larger over time while increasing its production rate of carbohydrate.
Stored energy in plants is often held as carbohydrate in long ‘chains’ of sugar molecules, starches, in what botanists call Amyloplasts, tiny organelles within plant cells. Amyloplasts are ‘plastids’, of which there are several closely related types, including chloroplasts, the organelles in which photosynthesis takes place; chromoplasts which produce and hold carotenoids, yellow and orange pigments that color particular tissues in floral parts and fruits, which have other lesser understood functions; while other plastids produce and hold various fatty acids, terpenes and lipids used in cell membranes, cuticles, epidermal tissues and as additional energy storage; still others serve some functions with proteins and others that aid with an orderly process of cell senescence, the recycling of dead or damaged cells.
Plastids are now understood to have once been free roaming organisms that became ‘included’ inside modern cells. They contain bits of their original DNA that is unique to them. By incorporating these former independent organisms these more complex cells gained functions that they never possessed before or greatly enhancing previously less effective capacities. Most plastids are capable of dividing and replicating themselves inside of a given cell and, depending on the species of organism, will do this to a greater or lesser extent. In the cells that comprise the parenchyma or ‘ground tissue of the Agave’s heart, Amyloplasts do this to an incredible degree which results in its massive starch rich structure, similar to a gigantic potato. Once flowering is triggered, this process of carbohydrate sequestration is reversed and the the starches are broken down into sugars as needed, by enzymes the plant is producing in far greater numbers. These simpler carbohydrates, sugars, are then transported to the mitochondria in the actively dividing cells of the meristem, and the new cells it’s formed. The Mitochondria extract energy when they burn/oxidize the sugar, adding that from the ‘broken’ chemical bonds to the organic battery of ADP, by adding another phosphate group, turning it into ATP (Adenine Tri-Phosphate). This is transported to specific sites within the cell where it breaks back down into ADP again, releasing its ‘electrical’ energy to power the growth processes in the cell, collectively powering the Agave’s phenomenal growth spurt.
Starting its Upward Journey…Slowly: the Limiting Factors of Water & Nitrogen
Over an Agave’s immature years, each leaf initiates one after the other in a uniform, spiraling pattern forming and expanding the rosette, separated by very short vertical spacing. Over the years its slowly extending stem swells forming the heart in a compact, 3-dimensional structure below the meristem. The oldest and smallest leaves, at the base of the rosette, nearest the ground, becoming shaded, no longer able to contribute to the whole, other than by ‘sacrificing’ themselves shriveling up and adding their moisture, nutrients and carbohydrates back into the ever growing plant, their desiccated fibers and structures still attached, often out of sight. And so the process continues, the meristem gradually increasing in diameter as the ‘heart’ expands around, growing somewhat taller…until the flowering trigger is tripped.
I won’t get into much detail here, yeah, sure you’re thinking, but it is important to know that Agave follow a different photosynthetic pathway than do the vast bulk of the temperate plants that we are more familiar with. It is called Crassulacean Acid Metabolism, CAM. Two other processes occur in plants, C3 which utilizes a 3 carbon organic acid in its process, is way less efficient in terms of water loss, but produces much faster growth. C3 evolved ‘first’ when plants were limited to an overall wetter landscape. It is the dominant ‘path’ and the most ancient form of photosynthesis in plants, the others being variation on its essential ‘theme’. The C4 process, utilizes a 4 carbon organic acid, separating its ‘stages’ physically within the leaf to reduce wasteful respiration and its consequent water loss. CAM separates the same two stages over time, creating its organic acid during the day, while utilizing the sun as a power source, then opening their leaf stomata at night, when ambient temperatures are lower, to draw in the CO2 and complete the process of carbohydrate synthesis. This limits the presence of Oxygen which can trigger the wasteful reversal of the process, respiration, in C3 and C4 plants, that results in the loss of water out through the leaves stomata. The C4 pathway is most commonly utilized by dry-land grasses, CAM is most commonly found in succulents and other desert plants, and it is the most conservative of the three in terms of water loss, which is very important to arid country and desert plants. Water availability and heat tend to go hand in hand, water becoming less available overall as regional ambient temperature climb. Water is the most limiting factor under desert conditions for plant growth, though it is not the only one.
Coarse mineral soils with a low level of organic matter are common to deserts. This has the further limiting effect on growth as these soils are often low in Nitrogen. Clay, very fine soil particles and organic matter have a greater capacity to ‘hold’ Nitrogen. Desert and other poor soils often get around this somewhat by the mix of plant species that comprise their communities and they do this by supporting nitrogen ‘fixing’ plants, plants that ‘fix’ atmospheric Nitrogen into the more available form of Ammonia. Desert areas tend to have a higher proportion of the plant species with this capacity than do those areas with finer more organic soils. You need to understand that plant growth is dependent upon the availability of nitrogen because it is essential in the synthesis of proteins and proteins are a major building block of all living organisms. Insufficiently available nitrogen results in weak, slow, growth. This becomes an even bigger factor for a plant like an Agave when it is in its flowering phase as it is growing an enormous amount of new tissue in a very short time in an environment in which nitrogen is more limited. Now while the soils where Agave montana is native have a significantly higher organic component and the capacity to retain more nitrogen with it, the enormous amount of growth it needs to accomplish this, is beyond its soil’s capacity to support and its roots to gather. So, in a way similar to its ‘mining’ its own tissues for water and carbohydrates, it recycles the nitrogen from proteins in no longer needed tissues, cannibalizing them. It robs it from the proteins in its leaf tissues, from anywhere it can get it, because after all, once it has finished flowering and producing its protein, carbohydrate and oil rich seeds, it dies. Those same ripening seeds contain Amyloplasts for starch storage and Elaioplasts for synthesis and storage of fatty acids and lipids. Seeds are nutrient and energy rich/expensive structures.
This isn’t such a strange process. Agaves did not need to ‘come up’ with an entirely new metabolic capacity. Most cells contain a structure inside them called a lysosome. These tiny organelles essentially digest damaged proteins within the cell utilizing acids, breaking them down into their component amino acids which are then made available to the countless ribosomes that populate every cell’s interior. Ribosomes are especially abundant on the membranes of a cell’s rough and smooth endoplasmic reticulum where particular proteins are finished and folded to fulfill the cell’s needs. In an Agave undergoing flowering the meristem’s need for amino acids and proteins would seem nearly insatiable, as it in a very real sense digests itself to flower and reproduce. This is where the necessary Nitrogen comes from. It is extremely well conserved. Accumulated over the years from the soil available to it, harvested by nitrogen fixing bacteria living in association with legumes and other species with this invaluable capacity, an Agave scrupulously gathers Nitrogen to itself.
All of these cells, with the exception of the more structural and fibrous Sclerenchyma cells, are alive in the Agave. When needed to supply the requirements of flowering, cells are selected and sacrificed in an orderly way. I’ve observed a similar process in Bananas which when under drought stress sacrifice older leaves/tissues to sustain younger ones, supplying their slowed metabolism the banana plant growing toward maturation and reproduction. All multi-celled organisms possess the capacity of apoptosis, which is the ‘programmed’ death of particular cells. This happens within most organisms when whole cells or tissues are no longer needed or have exceeded their programmed lifespans. For a flowering Agave, its leaves and heart are no longer necessary to complete flowering and seed production. Additionally living organisms are in a constant state of flux, animals even more so, continuously ‘recycling’ themselves. Within cells are other plastids called gerontoplasts which regulate the breaking down of dying or sacrificed cells. There is an order to this and the entire process occurs efficiently so as not to waste resources. Agave are remarkable ‘recyclers’ repurposing their own component parts they need from their own cells and tissues.
The Shift: ‘Foundation’ Completed, the Skyscraper Rises
When it is tripped the ‘balance’ and rate of growth shifts dramatically. The spiral pattern of growth is followed though modified. From here on all growth will be focused on flowering with no more expansion of the basal rosette, the ‘heart’ or the meristem. I suspect that the process of adding new roots is suspended, or at least reduced, as well, though I would expect that hair roots which in most plants are continuously shed and grown as they search out water and nutrients, would continue doing so. All, or the vast bulk of the available resources, will be utilized whether they are contained within the Agave’s existing tissues or drawn from available soil water for the extension of the peduncle or flowering scape itself, the flowers, its nectar and the seeds that will be produced. Photosynthesis continues in the now quickly extending green tissues of its peduncle and closely held bracts, the cells exposed to light developing choroplasts, adding to the capacity of its leaves. All of this supports the explosion, the massive surge of growth, rising from its meristem. The peduncle ‘shoots’ upward as a spear carrying the rapidly dividing meristem with it at the base of its ‘crown’, cells initiating from it.
As the peduncle grows taller the leaves are reduced to thiner, adpressed bracts, continuing in their spiral pattern. Each successive bract is separated by a vertical extension of the peduncle, comprised of what botanists call ‘ground tissue’ made up of relatively simple and uniform parenchyma cells. It is strengthened and reinforced with closely packed fibers of Collenchyma and Sclerenchyma cells, providing the vascular and fiber cells that add considerable tensile strength to this tall, rather fragile appearing structure. Sclerenchyma cells throughout the Agave effectively ‘die’ at maturity their added strength coming in part from their rigidity. This pattern continues uniformly to its ultimate height. The new growth emerges as a ‘spear tip’, the apex leading the way, growth lagging slightly behind as as you measure outward from the center to the perimeter of the meristem. The extending peduncle is not pressed up as if out of the ground from below, but emerges from the meristem as it ‘rides’ up the peduncle like a building rising floor by floor. Bracts form following the same spiraling pattern from the leaf primordia atop the growing meristem.
Once a given height is reached, for Agave montana probably something over 12’, will begin ‘releasing’ a series of secondary branches or peduncles, which will extend out perpendicular to the stem, horizontal to the ground, and along this will form tertiary branching which will carry the flower buds themselves on their individual pedicels. This happens in a way similar to Palms, another group of Monocots, in which the Palm’s inflorescence emerges from just below its crown as a branched structure. Like the Palms these branches are ‘determinate’ in nature, without apical buds, expanding only to a set size, their overall length and the amount of tertiary branching set as well. The few pictures that I’ve found on line of this species flowering show an abbreviated compact panicle structure, the entire thing possessing a heavy, dense, even stubby, quality. Each secondary peduncle will emerge in the spiral pattern followed by the bracts emerging from their axils, or points of attachment, in a manner similar to many thousands of other plants. Organisms all tend to follow patterns whether these are coded into the DNA, then translated into RNA to produce the necessary proteins, which are then organized, by other less understood ‘genes’, into these structures, visible and not; or by some even less clearly understood process of morphogenesis which follow less clearly understood patterns. By whatever mechanism, patterns are followed. However the constituent parts/cells are assembled, the end result is always a recognizable species, with heritable characteristics. An Agave seed will never grow into a different Agave species or vary beyond a limited morphological range…unless induced through physical damage, or by us chemically or via radiation.
Agave will not respond to delaying tactics. Once triggered, the process continues unabated. It cannot ‘try again’ the next year. Its metabolic and growth processes have shifted, irrevocably. Cut the flowering stem back or down and the sweet nutritive flow that powers it, continues pouring out on to the ground if not collected for its use as it sometimes is for a sweetener. If allowed to finish flowering any remaining ‘reserves’ in the heart, which will be relatively few, cannot be redirected to its own vegetative growth. That option is shut down through apoptosis another internal switch. The only thing in its future is decline and death. It would be like asking a spawning salmon to ‘hang around’ the waters of its origin for another round of egg laying, later, its energy reserves and even its flesh spent in the effort to return to the waters of its origin. It literally can’t.
Many other Agave have the capacity to produce offsets or ‘pups’ at and around their base from relatively short lengths of rhizome, stem material carrying a bit of meristem at its extending tip, around the mother plant. For some this occurs only during their youth, for others there is a ‘rush’ to produce them in their flowering stage, while others still are more methodical producing them more or less continuously over the mother’s lifespan. This can result in significant colonies. In others, like Agave montana, they are solitary, producing no offsets….Ever. Every species has its own individual reproductive strategy, while much of it may be shared across a genera, they can vary in the particulars. Those species that produce only by seed are more dependent on their growing conditions and the availability of their pollinators. A ‘bad’ year for them when they are flowering can mean a failure in their one chance to reproduce, where those species that form clonal colonies have multiple backup options…no species survives and continues on as a single individual. There are minimum thresholds if a species is to survive and increasingly, that is becoming more difficult for many species across their native ranges.
Bats and Late Season Pollination of Agave montana?
Agave montana belongs to the subgenus agave, sometimes abbreviated as, subg., agave. These are the species that produce a branched, paniculate, inflorescence. The other subgenus, littaea, grow their inflorescence as a simple spike.
(The use of these two subgenera is not accepted by all botanists as the groups are paraphyletic, incomplete genetic lineages made on a morphological criteria, branching, a trait that is genetically ‘scattered’ in the genus. There is even considerable disagreement about where the genus itself belongs, a situation complicated by the genera’s relative youth, 8-10 million years, the ease with which hybridization between species (and even related genera), takes place, the incomplete lineage sorting, work that remains yet to do by botanists and long generation times. I am simply intending to use the subgenera descriptively.)
What seems important to me is that the paniculate inflorescence of members of subg. agave are particularly well adapted to bat pollination, specifically, the two native Mexican nectarivorous species that literally fly a ‘circuit’ north through Mexico in and around the ‘western’ Sierra Madre Occidentale, into the the southern portion of Arizona’s Sonoran desert then, turning easterly, follow along the Rio Grande before turning back south through the Sierra Madre Orientale. They are not resident along this path, they are migratory, and on a schedule that follows the blooming cycle of many of the taller growing cacti, like the Organ Pipe Cactus and Saguaro as well as many Agave. They do spend extra time in the northern portion of the range raising their young slowing their annual circuit. These branched, paniculate structures of this group of Agave, allow the bats to more easily access the individual flowers, a process more difficult for a bat when an Agave’s inflorescence is in the form of a tightly held spike. New world, nectarivorous bats do have the ability to hover in front of flowers unlike other bats, but don’t seem as ‘acrobatic’ as hummingbirds. Bat pollinated flowers tend to open their flowers and release nectar at dusk in preparation for for night pollinators like bats and moths. Bats utilize echolocation to find flowers, so bright flower colors are less important and such Agave tend toward paler flowers. There are also difference in the scent of their flowers, which are more unpleasant to us, a kind of over-ripe scent attractive to these bats. Overall bats and hummingbirds tend to visit plants that are heavy nectar and pollen producers when compared to those that are exclusively insect pollinated. Pollen contains more of the protein they require. Check out this link on nectarivorous bats.
Are bats a significant pollinator for this species? The fact that this Agave has bright yellow flowers with contrasting ‘red’ bases creates a vivid inflorescence, a characteristic offering little utility in attracting bats though its branching would indicate that it has adapted at least in some way to accommodate them. From what I’ve read their flower display is attractive to Hummingbirds, at least in Texas, where these have gained some popularity as a garden plant since its introduction. Across its native range in Mexico there are more hummers and I imagine bees, native or otherwise, butterflies and moths active over a wider span of months than there are in the States. There are 19 species of Hummingbird native to Tamaulipas, 14 to Nuevo Leon, 21 to San Luis Potosi, 22 to Querotaro. Included in those lists are our own Rufous and Annas as well as the less frequently found here, Allen’s. Given the right weather conditions when it blooms here it would seem that it could be adequately ‘serviced’, as it appears to be more general in its pollination requirements….
A relatively unique characteristic of Agave montana comes into play here, they begin their flowering cycle in the Fall! Yes, they do! They extend their massive, thick peduncle some 10′ or so and then stop! There are a handful of montane species apparently that does this. They shut down over the winter and wait it out, their meristem protected within the tissues of the thick peduncle and heavy, overlapping, clasping, cover of bracts. In this dormant state they are more ‘armored’ against damage. They have a ‘trigger’ sensitive to cold and/or day length to turn them off and another one, to turn them back on in the spring. In its home range it suspends growth before it reaches the height of its first branches, then in Spring adding the remaining length to its peduncle, all its compact branching and beginning to flower. This Agave’s unique flowering strategy certainly explains its ‘delayed’ start here in Portland.
Now Just Step Back and Get Out of the Way!
The speed with which the peduncle extends is almost shocking, especially in the relatively slow moving incremental world of CAM plants, but understandable if you take time to think about it. It is not limited by the energy it can photosynthesize from day to day, it relies upon its ability to convert its storehouse of carbohydrates, the other necessary nutrients held in its tissues and the water in its heart and leaf tissues, limited instead by its ability to metabolize the needed organic acids and enzymes, its capacity to create and conserve ATP, the tiny chemical battery packs that power cell function. Photosynthesis is now only a small supplemental source. We are taught about the ‘miracle’ of photosynthesis in plants and its ability to produce carbohydrates chemically capturing solar energy and then tend to leave it at that…but plants can no more prosper off of carbohydrates alone than we can. From its own tissues and its heart an Agave draws the needed amino acids and/or component parts of the proteins, lipids and enzymes that it requires to supply and regulate the growing of cells, tissues and structure of its rapidly developing peduncle. Plants produce most of what they require from very limited raw materials, while animals like us must consume our nutrients in more complex, more complete form, vitamins for example. Recall the harsh limiting conditions facing Agaves, and you can begin to see the enormity of the problem of converting old structures and tissues into new, its soil environment and its metabolism unable to supply what is needed without utilizing the storehouse of its old tissues.
The now mature meristem, ‘calls’ on the rest of the plant for what it requires to grow the inflorescence, producing the structured matrix of what botanists call ground tissue from parenchyma cells, reinforced with tightly spaced fibers for strength, within which are, scattered elongating bundles of vascular tissues, made up of continuous chains of specialized vessel and trachea cells. The cell walls of these are thickened and strengthened to carry the uninterrupted supply of what the meristem and developing cells and tissues need. Unlike the woody stems and trunks of Eudicot trees and shrubs, all of this stem tissue remains alive beyond their maturation and so require an unbroken supply of water and nutrient to maintain itself, each cell taking in what it needs to meet its particular requirements to maintain itself and carry out its function. Each cell, other than the specialized vascular cells, ‘work’ independently to meet their metabolic needs, having the capacity to produce the enzymes, proteins, lipids and ATP they need on their own. Vascular cells have evolved depending more on their neighbors to meet some of these requirement as they grow and elongate. The outer sheathing epidermis is ‘green’ its cells populated with chloroplasts, fully capable of photosynthesizing on their own. The ground tissue within, shielded from light, contain no chloroplasts having lost their chlorophyll and been converted for other uses. There is otherwise no ‘centralization’ of production only a uniquely efficient conversion and distribution system providing cells with materials it must then synthesize…an amazingly efficient and effective logistical supply system…organic…’just in time’.
This is from a Facebook post I made on Oct. 18:
“Monty has reached 113”, 9’ 5”! Recently it has been adding about 2 inches per day. How much new tissue is that? From high school geometry the formula to calculate the volume of a cylinder, in this case of Monty’s peduncle, is Volume = pi x radius squared x height! Monty’s radius is 2 3/4”. For each inch the peduncle extends it must create 23.75 in.³ of new tissue, so 47.5 in.³ per day at its current rate! Compare this to when Sharky, my Agave x ‘Sharkskin’, flowered in 2016 with a 2 1/2” diameter peduncle. Sharky produced only 4.9 in.³ of new tissue per vertical inch of extension, somewhere between a quarter and a fifth of what Monty is doing.. Sharky was, however, faster, growing at a rate varying from 4″ to as much as 9″ per day, adding between 20 and 45 in.³ of tissue.
To that date Monty had added between 1 1/2″ and 4″ per day to its height so that’s a lot of tissue to create! It is all the more amazing when you consider that it took 20 years to create the rosette structure and heart.
There’s another question I wanted to address and that is what powers this upward flow of energy and vital fluid? There is no canopy of leaves, or significant green tissues above the apical meristem drawing it up, no appreciable amount of stoma, which through their water loss, create a negative vacuum pressure in its vascular system great enough to draw fluids, nutrients and solutes up against gravity. In fact, if flowering Agave follow the CAM photosynthetic path with its stoma closed during daylight hours, there should be no flow at all during daytime hours, but there is. When the flowers themselves have matured and open there is heavy nectar flow, filling and flowing out of each flower’s perianth. Clearly, something else is powering this flow…and I suggest that it is due to the physical and chemical characteristics of water and its ‘energized’ fourth phase. See my discussion of this in my previous post, “Life Inside the Cell – Waking Up to the Miracle, part 1a”, specifically the section subtitled, ‘Water: the ‘Magical’ Ingredient’. The fourth, denser, phase, unique to the water molecule, is created when water comes in contact with proteins, such as those comprising so much of cells and vascular tissues. In organisms. This results in a natural flow through vessels constructed with proteins. This phase and this action is triggered by certain frequencies of light including the infrared band, heat, creating a phase shift in the water itself. Organisms, their tissues and living cells contain a high level of energy in their structures requiring relatively minor shifts and inducements to push them into action, releasing energy as they flip from phase to phase. See Gerald Pollack’s book, “The Fourth Phase of Water: Beyond Solid, Liquid and Vapor”.
Agave are well adapted to their harsh conditions. Such conditions have been shaping them for thousands of generations. Their flowering process, once initiated, moves with a certain inevitability, initiation to ripened seed in one sustained effort. By then whatever nutrients and water might still reside in the old rosette, is abandoned, the plant itself dead. The rosette’s toughness and resistance to the elements may preserves it, but…dead is dead, whether it looks like it or not.
With all of the barriers to successful reproduction that face Agaves, why do they ‘spend’ so extravagantly on a massive and tall inflorescence? Obviously their strategy has been successful for them, but couldn’t they be more so with less expenditure? Couldn’t they conserve themselves and flower a little bit each year? like a Yucca? Well then, they wouldn’t be an Agave. Those species that live in deserts follow the same ‘thrifty’ plan that many other desert residents follow, spacing themselves out to reduce competition for very limited resources, their height allowing them to stand out as beacons to pollinators in a landscape that offers relatively few widely spread options? Montane species like Agave montana live in relatively dense communities with Oaks and Pines and maybe their shorter, thicker peduncles are a response to that living in a landscape that is richer in species, more densely covered, with richer and moister soil. Whatever the reason we will likely never know exactly what it is. It is important that we know what they are doing and how, so that we can assure their survival and success into the future. Agave have been successful for several million years…that is a substantial track record and absent our disruption and reductions of their native habitat, they would no doubt continue thriving, adapting and evolving for millions more. We should attempt to understand what we are doing in and to this world. If nothing else, little attempts like this to understand the larger living world can open our eyes to both its miraculousness and fragility, suggesting a path to follow to assure the health and vitality of the many species and ultimately of our own as well.
Whatever happens, whether, Monte, my Agave montana completes its flowering successfully or not, it has been a worthwhile experience. Whatever the out come, it will pass. Many plants, due to their longevity and our ‘relationship’ with them, their stature and roles in our garden, the time and energy we’ve invested in them and our fears surrounding their survival, assure that we’ll have a little pain when they pass. Monte has been a prominent garden member, one noticed by many visitors and passersby over the years. My wish for seed and descendants is a little selfish on my part as not every individual can survive or should. Life must make room for other life to assure that the larger process can best continue. Like ourselves here, this Agave is an interloper and its life is not historically supported. Its chances of forming a viable long term population, in such a volatile landscape, is vanishingly small, as cities are defined more by disruption than by the processes and energies of nature. ‘Monte’ will vanish, the urban landscape will remain unsettled and its prospects difficult to even imagine. We humans represent both a threat and the possibility for a future as we sensitize ourselves to the places we live and the plants that we grow.
Watch for a followup post, probably next summer, ’20, with a look at ‘Monte’s’ winter, spring, summer finish to its flowering. I’ll be looking closer at the conditions leading up to and present during its flowering…stay tuned!