Pollination: Sensational Sky Islands Sexual Strategies!

Spring has arrived in the Sky Islands and we find our lives suddenly transformed by the ephemeral, yet powerful beauty of wildflowers.  Winter, save for perhaps a looming late frost, has vanished and in its stead is a new world - abuzz with life thanks to countless yellow, white, orange, purple, and blue blossoms.  Fortune, it seems, smiled upon us with ample-enough cool season rains and snows, spawning a veritable pageant of life in some areas. 

While our eyes, noses, and even our skin admire the delicate flowers adorning our deserts, grasslands, foothills, and riparian areas, this is an evolutionary fluke of sorts, though certainly one that has had and continues to hold implications for our own species.  Flower shapes, sizes, scents, and arrangements have been honed via natural selection - the driving mechanism of evolution - to attract not us but rather a diverse cast of pollinators that aid in the sexual reproduction of plants.  Take away these coitus conduits and many plant species would likely become extinct.  Thankfully, however, these co-evolved pollinator relationships continue to intrigue and dazzle the curious Naturalist.  Each year insects, birds, and mammals - to name some of the more common pollinator groups - provide sexual services for a wide range of plant species, promising future blooms that are sure to delight.

Perhaps it seems strange and foreign to humans that many plant species require the actions of animals to effect reproduction.  Judging by our 7+ billion world population we generally have no impediments in this arena!  Short of sperm banks and modern in vitro procedures, we generally accomplish the task sans helpers.   Given their lack of motility, however, our plant brethren evolved a number of fascinating ways to lure potential sexual couriers in, generally furnishing them with substantial caloric rewards.  Many flowers, then, are the ultimate in sexual advertisement, going far beyond even the raciest of perfume or lingerie adds.  This is the stuff of the seedier classifieds: “SSF (single staminate flower) seeks hungry insect to transport pollen to sensual ovary for once in a lifetime Spring tryst...”

Before we enter this botanical Bourbon Street, however, it bears recognition that many plants are able to reproduce via the wind, foregoing any or most animal assistance.  Prior to the invasion of terrestrial habitats by invertebrates, plants such as Mosses, Club Mosses, Ferns, and Horsetails evolved to take advantage of water and wind to help effect reproduction.  Once Conifers followed these predecessors onto terra firma they too evolved to spread their pollen (the relative equivalent of spores in the case of the aforementioned primitive plants) via the whims of the wind.  Thus, such species as Arizona Cypress, Alligator Juniper, White Fir, and Engelmann Spruce, to name a few, employ the vagaries of the wind in order to effect pollination and, thus, sexual reproduction.

Pollen contains the male genes of a plant and requires coupling with the ovary of an individual of the same species.  Once a grain of pollen reaches the ovary it grows a pollen tube down to the ovules or eggs in a process vaguely similar to sperm swimming to eggs.  There in the ovary the ovules are fertilized, develop into seeds, which help to ensure the survival of the species if and when they eventually germinate and grow into sexually mature plants.  

Preferably such sexual reproduction is accomplished by crossbreeding between two plants, rather than self-fertilization within a plant. In other words, the pollen from plant A reaches the ovules of plant B.   Such exchange of genetic material between two plants allows for variability, affording a greater range of survivorship of certain individuals within the ever-changing environmental conditions of the world.  Still, some plants occasionally self fertilize, while others are mostly or entirely cleistogamous.  In the latter case a single, unopened flower fertilizes from within its own structure, foregoing the possibility of outcrossing.

Most flowering plants do employ animals in the process of reproduction.  What, then, are some of our more intriguing pollinator systems in the Sky Islands?

Perhaps my favorite one is that of the Southwestern Pipevine (Aristolochia watsonii).  You might wander and explore our arroyos, Mesquite Bosques, and riparian areas for quite some time before encountering this rather inconspicuous vine in the Birthwort Family, Aristolochiaceae.  Many members of this family dupe potential pollinators - mostly carrion-phile insects, to their blooms via fetid odors coupled with a deep maroon color that approximates that of rotting flesh!  Our Pipevine lures in Ceratopogonid flies, “no-see-ums” that feed upon the blood of mammals - including us.  It seems that the pipe-shaped flowers mimic the shape, texture, and odor of a mouse’s ear.  No, that was not a typo!  The intrepid fly while trapped overnight stumbles upon pollen, not blood, only to, hopefully, repeat the feat at another Pipevine flower.  Weird.  Look for the Pipevine Swallowtail as a strong hint that its namesake host plant is sequestered nearby.

More conventional are a number of plants that “specialize” in Hummingbird pollination.  Tubular or funnel-shaped flowers, particularly red, orange, and yellow ones, scream “come hither” to the voracious hummers.  The long corollas (the sum of all the petals of the flower) generally prohibit entry to all but the longest of animal appendages, allowing these “jewels of the sky” to mostly monopolize the nectar that is so vital to their existence.  

As I write, the extensive Ocotillo (Foquieria splendens) bosques at Raven’s Nest, our Nature and Wildlife Sanctuary, are at the verge of exploding with the red of their copious flowers.  These are a prime example of the aforementioned pollinator system.  The Ocotillos possess long, tubular, red blossoms that bloom more or less regardless of Winter rains.  Meanwhile, Hummingbirds - Broad-billed, Rufous, Black-chinned, Anna’s, and others - amass in hungry anticipation of this sugary feast.  The blooming of the Ocotillos and the migration of the Hummingbirds is perfectly timed to produce both pollination and well-fed migrants or breeders, depending upon the species of bird in question.  Either way, look for the yellow, pollen-speckled foreheads of Hummingbirds this month.

At the other end of the spectrum are plants that welcome a wide range of animals for their pollinator services.  One fine example of this are the Agaves that adorn our deserts, grasslands, and chaparral.  Palmer Agave (Agave palmeri) springs to mind in this realm.  During the often climatically onerous months of May and June the large, asparagus-like (Agaves have been reassigned to the Asparagus Family, Asparagaceae) stalks burgeon forth from the heart of these wickedly-armed plants.  Given that each Agave likely amassed enough sugars and other resources in order to bloom over the course of several decades they then throw all caution to the wind in a pollinator party extraordinaire.  

The semi-showy flowers adorn the outer parts of branches that emanate from the behemoth stalk.  Their arrangement as well as the characteristic odor - that of ammonia or rotting fruit - seems designed to attract nectar-feeding bats.  Both the Mexican Long-nosed and Mexican Long-tongued Bats heavily visit the blooms of Palmer Agave, even timing their migrations to coincide with its flowering season - mostly July through September.

Beside these 2 bat species, Palmer Agave also hosts bees, ants, Hawkmoths, beetles, Orioles, Doves and others.  These too aid in the sexual exploits of the Agave.  Its a sort of hedonistic effort to cross-mate.  Why not when you’re destined to die afterwards anyway?  For Palmer Agave invariably deceases after flowering, each plant relying on successful pollination to outcross with another of its species.  To hedge its bet, however, this species also produces offsets, which are genetic clones of the parent plant.  If any of these individual Agaves reaches the sexual finish line, then the species endures.

While there are seemingly countless other fascinating flower tales to tell, space is, alas, limited.  Allow me to part by posing you a question.  Why is it that we humans have ourselves evolved to use the sexual parts of plants - particularly the flowers themselves as well as their aromas - as sexual attractants for each other?  Perhaps flowers are the ultimate red-light district neon sign advertising availability and desirability.  Bouquet anyone? 

Vincent Pinto and his wife, Claudia, run RAVENS-WAY WILD JOURNEYS.  RWWJ is dedicated to the preservation of the incredible biodiversity in the Sky Islands, including Backyard Habitat Consultations.   You can call Vincent at (520)425-6425 or e-mail at ravensnatureschool@gmail.com  

AMAZING MADREAN PLANTS

The biodiversity of our Sky Islands is truly astounding.  Here at the meeting point of 4 major bioregions - The Sonoran Desert, the Chihuahuan Desert, The Rocky Mountains, and the Sierra Madre Occidental - we have towering and isolated mountain ranges that loom as mesic, forested beacons above the drier interceding habitat of grasslands and deserts.  At our relatively low latitude - for a temperate region - of about 32 degrees we already are candidates for high levels of diversity.  Add to this the Galapagos-like element of our Sky Island ranges - isolation that contributes to evolution - and the seemingly competing influence of connectivity that the stepping-stone arrangement of our mountains facilitate and the resultant mix of flora and fauna is truly astounding!

As a seasoned and professional Naturalist, Ethnobotanist, & Wildlife Biologist I am still discovering Sky Island plant species new to me with each passing year.  More importantly, I continue to forge lasting and meaningful connections with the species whose acquaintance I’ve already made.  Among my favorite plants are those whose ranges barely extend into our region.  Often these are more tropical species generally less tolerant of freezing temperatures than their Sky Island compatriots.  Thus,  Madrean plants rub elbows, so to speak, with their temperate and desert brethren.  Here I hope to introduce you to a few plants living along the edge - our edge.

Given my past explorations in the wilds of Florida and the Caribbean, I was initially floored to encounter an engaging little plant seemingly more suited to those climes.  Many years ago I found myself exploring the incomparable beauty of Sycamore Canyon along the border with Mexico.  Having heard tales of its beauty and profusion of life I was not disappointed with its otherworldly character.  Two plants in particular caught my keen eye as I meandered along Sycamore Creek during the verdancy of Monsoon season.  

Casting a glance towards the familiar One-seed Junipers lining the canyon bottom, I noticed intriguing little clumps festooned upon certain branches.  Not quite believing what my brain was already registering I indeed confirmed the presence of a member of the Pineapple Family - a bromeliad!  Later research proved this to be Ball Moss, an epiphytic member of the Bromeliaceae - Tillandsia recurvata.  The range of this species extends from south central Arizona - the location of Sycamore Canyon - all the way across the southern tier of states and into the Caribbean.  Indeed, I realized that I had encountered this species on numerous occasions in Florida, and likely in Jamaica as well!  For perspective, such epiphytes - represented by a number of plant families - become at once common and spectacular in the lower clutches of Mexico’s rightly famous Barranca del Cobre, Copper Canyon. 

Here, they lurk on the fringes, inhabiting almost exclusively Juniper Trees - now referred to as Coahhuila Junipers (Juniperus coahuilensis).  Only once have I witnessed a Ball Moss growing in a rock instead of a Juniper.  They render an otherwise Great Basin 

Desert-esque scene into a subtropical one.  They are commensals upon the Juniper, meaning that they have no measurable adverse or positive effect upon their hosts, while they themselves indeed benefit by living upon the shady, moister branches.  Ever the curious Ethnobotanist, I nibbled a few leaves from a hardy plant the other day at a site a mere handful of miles from Raven’s Nest, our 42-acre Nature Sanctuary near Patagonia Lake.  The taste was not unpleasant - a bit astringent - and I’m still here to tell the tale!

During the same Sycamore Canyon saunter I met with an even more rare Sky Islands botanical wonder.  Growing in a canyon wall cleft was a primitive plant whose next nearest populations reside in 1200 miles away in Texas and about 300 miles south in Mexico, near Yecora in Sonora!  Whisk Fern (Psilotum nudum) indeed seems an anomaly akin to Ball Moss.  One expects such a rare, primitive fern to show up in the Gondwanaland relict forests of Queensland more than in our borderlands.  My initial impression of this strange species was that of a horsetail crossed with a fern.  The family Psilotaceae contains only 2 species, including the one in Sycamore Canyon.

Much easier to locate and admire is the Mexican Blue Oak, whose range, never-the-less is very constricted in the U.S.  Despite the well-known proclivity of members of the genus Quercus (i.e. Oaks) to hybridize, Quercus oblongifolia is one of our easiest species to identify.  Its lowland habitats on the fringes of grasslands and canyon mouths, combined with the bluish cast of its notably blunt-tipped leaves readily distinguishes it.  Mexican Blue Oak only enters the U.S. in southeast Arizona and extreme southwest New Mexico.  

Recently my wife Claudia and I stumbled upon a truly dazzling one while exploring the more hidden canyons near our home.  This venerable tree must be hundreds of years old given the likely rather slow growth rate of Oaks in our region.  Its DBH - diameter at breast height - is well over 3 feet across!  Nor does it lack in the character, given its nearly horizontal bole and the fact that its own trunk has a firm hold on that of a young Netleaf Hackberry (Celtis reticulata).  We were thrilled to encounter this magnificent tree, especially given the double gauntlet that this and other plant species ran two years ago of drought and extreme freezing temperatures.  It renders our usual haunts rather unusual in fact.

  

Rounding out our brief exploration of the plants that, barely, call the Sky Islands home is  a more familiar face.  Anyone who’s spent significant time hiking in the canyons and rocky foothills of the Sky Islands has likely come across a distinctive member of the 

Bean Family - Southwestern Coralbean (Erythrina flabelliformis).  It too is frost sensitive and often gets killed back to the ground during severe Winter weather.  Thus, we merely see it as a tall shrub for the most part in Arizona, which it barely breeches from the south.  In those warmer climes lurking near us in Mexico it regularly reaches respectable tree proportions.  

Once, while wandering through the Tropical Deciduous Forests just outside the colonial town of Alamos, Sonora I stumbled upon the distinctive and brilliantly crimson seeds of Southwestern Coralbean.  No, I thought, it can’t be, as the tree from which the seeds emanated towered a good 40 feet above me and sported a DBH of about 2 feet!  Subsequent reading, however, confirmed that this species regularly attains tree size where its not limited by freezing temperatures.  Local cultures even value it for lightweight furniture.  Thus, even when a plant species from warmer climes invades our Sky Island region, it may express itself quite differently than in the heart of its range. 

Had I more time and space I would love to wax poetic/scientific over a much longer list of fringe plants.  Far too many people either seem unaware of the botanical treasures at their doorsteps and/or simply take them for granted.  In a day and age of increasingly imperiled biodiversity, we feel it’s imperative to not only take notice, but to sing the praises of both the common and the rare wild things that enrich our lives.  Consider, then, finding and familiarizing yourself not only with the few species mentioned above, but also with the Yellow Trumpets, Mala Mujers, Madrean Yuccas, and Sayas that collectively constitute our unique subtropical flare.

Vincent Pinto and his wife, Claudia, run RAVENS-WAY WILD JOURNEYS.  RWWJ is dedicated to the preservation of the incredible biodiversity in the Sky Islands via Nature Adventures and Educational programs - including Wildflower & Botany tours.  You can call Vincent at (520)425-6425 or e-mail him. at ravensnatureschool@gmail.com