Relevant review of basic flower structure: POLLINATE HERE
Fieldtrip rained out yesterday, so in honor of the drizzle, here’s a wet weed in flower a little this week. Pickerel Weed is one of those South Florida beauties familiar also to frosty northerners, My earliest recollections of it come from maybe age 10 along Canadian lake shores and rivers.
Funny how aquatic plants, Sagittaria, Wild Rice, Water-Chestnut, Cat Tails, and many more provide so much starchy food. Pickerel Weed has served as sort of a “grain,” the seeds nibbled like nuts or ground for meal. But….reinforcing my usual spirit, please don’t eat nature…note that one of the few historical medicinal uses is as a pre-European oral contraceptive. “We’ve been living natural and all out here off the grid but just can’t make a baby.”
And some nature-eaters have suffered allergic mishaps and even intoxication, not to mention whatever water pollution sequesters in the plant.
A bee by name of Dufourea novaeangliae likes Pickerel Weed, gathering pollen for its brood exclusively or nearly so from those purply-blue blossoms. The bee burrows into stream or lake shores near the PW. Not too surprisingly, the bee’s geographic range is similar to that of the plant, which, however, has a broader distribution, especially to the south. Additional visitors include several more types of bees, butterflies, moths, and even hummingbirds. The preferred customers are Bumblebees.
Bumblebees engage in a type of foraging called traplining, where they visit the same traps (food sources) repeatedly. The stops around the trapline itinerary must provide awards over an extended period. The PW flower spike makes hundreds of single-day flowers during its long life, with some opening anew each morning as old ones become fruits. A patch of pickerelweed offers flowers for the entire season, with that big yellow spot on blue background apparently advertising, “open for bees-ness!”
So far, ho hum, that’s all textbookish, but also a nice buildup to the good stuff, so here we go. The flowers have an unusual characteristic called tristyly (TRY-style-ee), that is, they come with styles in three different lengths on different individuals. Helpful reminder: the style is the elongated part of the floral female unit, receiving pollen on its tip. Stamens make the pollen, likewise at their tips. So then, different flowers on different individuals with styles of different lengths receive pollen at different depths in the flower: outside the entrance, at the entrance, and deep within.
This may seem like this “wherever you drop off the pollen” flexibility accommodates many different pollinators, from ones who flutter outside the door, to those who push right on in. No doubt true. But there’s more to it.
Remember, it takes two to tango, and the stamens come in three lengths also. Now pay attention: Each flower has stamens of the two lengths that do not match the style length of that flower. Huh? Let’s say you have a short-style flower, then the stamens are of the middle and long lengths only, sans shorties. Got it? What are the stamen lengths in the mid-styled flowers? Answer, short and long. Another way to look at it is that each flower has three positions, short, middle, and long. One position is occupied by the style; the stamens occupy the other two positions.
Long style: stamens middle and short
Mid-length style: stamens long and short
Short style: stamens middle and long
But why? To avoid self-pollination. If a long-styled flower also had long stamens, those long stamens would deposit pollen onto the adjacent long styles in the same flower. Additionally the long stamens would dab pollen onto pollinators positioned to brush back off on long styles of other flowers on the same plant. Self-pollination is severe inbreeding, not good in humans, in Golden Retrievers, or in Pickerel Weeds.
And chew on this: a rhizome-connected colony of Pickerel Weed is one big sprawling individual genetically speaking, even if it looks like separate plants, so any pollen transfer within that extended colony is self-pollination. With the no-stamens-at-the same-length-as-the-style policy, the pollinator must carry pollen to a different genetic individual for effective cross-pollination. A long-styled colony must receive pollen from mid-styled or short-styled colonies. Cross-breeding is enforced just like island-dwellers court spouses from different islands.
Confusing? Naw, with tristyly you don’t pollinate your own flowers even though all the while you’re catering to diverse pollinators. Pretty slick for a swamp weed.