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Cuddly Cotyledons

This time of year every naturalist, armchair or otherwise, is enraptured with the stunning emergence of spring ephemerals. These delightful little splashes of color appear especially vivid after months of brown, gray, and white in the woods. But the more time I spend traipsing through the same woodlands and prairies, year after year, I’ve come to appreciate another ephemeral feature brought by the rains and rising temps: cotyledons! Cotyledons are the tiny, embryonic leaves that first emerge when a seed breaks dormancy, and often they can look strikingly different than the mature form of the same plant. Part of the difference “stems” from the fact that the cotyledon is essentially the last vestige of the seed phase of the plant’s life, before the more recognizable above and below ground organs develop.

Garlic mustard cotyledon
Flowering garlic mustard

This unique phase of the plant’s life represents something remarkable. We generally know intellectually that a maple tree grows from the seeds that rain down on winged samaras each spring (or fall depending on the species). But to look at the tiny cotyledon, and shift our gaze upward to the mighty mother tree who’s shed thousands of offspring this year alone, creates a tangible sense of the incredible odds the tree overcame to reach the canopy.

Maple cotyledon
Mature maples

The cotyledon represents the first breath, the umbilical cord between the plant’s life as an inert seed and its future as a metabolic powerhouse. The cotyledon provides the critical early "food" for a plant before the true leaves develop, one last contribution from parent to offspring before it must fend for itself amongst a crowded landscape of competing plants and voracious herbivores.

My first real appreciation for cotyledons came when I started to notice an abundant "mystery plant" along the nature trail here at Osborne. With the luxury of frequent field trips in May, and along with them frequent opportunities to watch the plant community develop, I watched as the two tiny leaves rapidly gave way to the rising stalk of a much more familiar friend.

Jewelweed cotyledon
All grown up and ready to cure nettle stings

Now, I celebrate the first tender green shoots of jewelweed as much as the first blooms of hepatica and songs of the spring peeper. I don't know why this particular tiny green thing caught my attention, but I think it's because I just plain thought it was cute.

Henbit with first true leaves above the cotyledon

Really, most of them are pretty cute. Most tiny things are, for that matter, when you really get in there and take a close look. But they do all look pretty darn similar. To be sure, it's generally difficult to identify a plant without the "true" leaves. Cotyledons serve an entirely different role in the plant's life cycle, helping to access nutrients already stored within the seed itself and transport them to the growing stem. They often photosynthesize, but not always. For instance, the cotyledons of some larger seeds, like walnuts, can (and often must) push through several inches of soil, in the absence of sunlight, before reaching the surface.

Sprouting black walnut

The bigger the seed, the more energy stored within, so the plants can "get by" on the cotyledons alone for longer. Smaller seeds, often annual plants, play more of a numbers game and rely on photosynthesis from the get-go. Where a walnut tree produces on average 800-1000 walnuts in a normal year, a common ragweed might produce as many as 60,000 seeds at the end of it's annual life cycle. These miniscule seeds are more vulnerable to the vagaries of wind (where did they land) and weather, with their early rations running dry quickly.

Common ragweed hastily making true leaves

Spring is an ephemeral season, an umbrella term really for the combination of ice-out, mud season, animal migration, woodland wildflowers, burns, morels, planting, high water, and severe weather. The sound of frogs singing in shallow pools left over from spring rains changes depending on the temperature, progressing from peepers to chorus frogs to leopard frogs as the mercury creeps higher.

Spring is a time of transition and fleeting experience. Cotyledons embody that concept as well as anything, rapidly disappearing when the plant can fend for itself. Some of them don't appear at all, in the case of "hypogeal" germination, like peas or corn.

In hypogeal germination, the cotyledons remain within the seed and push the radicle (embryonic root) out of the seed, acting as a transport organ for the nutrients locked up in the seed. But for those epigeal plants who "pull" the nutrients up into the sunlight, the cotyledon provides another fleeting experience on spring's march to summer.

They represent the joy of a woodland saunter, a reward reserved only for those who have the patience to view things in micro. They represent an invitation to come back, to watch life literally unfold with each passing day. They represent an assurance that the barren landscape of winter has let go, soon to be replaced by the humid, jungle-y, verdant mess that is the growing season.

Looking Back

April got very busy here at the CCCB! In terms of the workload, it always feels like April comes in like a lamb and out like a lion.

Classroom visits start winding down for a brief moment before field trip season starts showing up, but this year we got to do something special that was a little bit of both... School of the Wild! School of the Wild is a multi-day nature experience aimed at awakening an awareness of the wildlife and natural ecosystems in our area, developing an appreciation of the natural world, and encouraging a balanced environmental ethic and caretaker attitude concerning the earth.

Learning the art of the atlatl, a primitive hunting tool

This excellent idea is run through the University of Iowa's education department, who provides resources and logistics for providing a cross-curricular learning experience to students amongst Iowa's wild places.

This year, Starmont 5th graders got to spend an almost-week (Spring weather strikes again) at Backbone State Park. That week they learned about forestry, cartography, geology, history, biology, and ecology, while getting an ample amount of P.E. in kayaking, fishing, hiking, and throwing atlatls, all while taking moments to practice their writing and artistic skills with guided journaling exercises. We snuck more than a little math in there too, just to hit for the cycle.

"Can we eat lunch in that cave?" "....I don't see why not."

The next week the naturalists took a divide-and-conquer approach to accommodate field trips to Osborne and the annual Arbor Day tree plantings at each county school. Many thanks to the Fort Atkinson Nursery for the large trees, and the Iowa DNR for tiny ones to send home with each student!

Central students giving and receiving Arbor Day gifts

With wind and water combining to thwart a great many planned prescribed burns, we did manage to get one in on the north unit of the Motor Mill Historic Site. The later burn, after green-up, will hopefully help control some of the cool-season grasses that suppress the midsummer wildflowers and stately prairie grasses.

Looking Forward

April showers bring May flowers! May is Iowa Wildflower Month, and all it takes to celebrate is a little walk in the woods or prairies. Bonus points if you can spot a pollinator using said wildflower, of course.

One great spot to look at wildflowers is along the Osborne Park disc golf course, which wanders through our prairies (front 9) and woods (back 9). It's an open invitation, but on Saturday, May 14th, we'll be hosting an open disc golf tournament if you've got a competitive streak. The tournament begins at 9 AM with a shotgun start; register here or show up early that day when registration opens at 8:30.

The O.W.L.S. will have a chance to visit the Garnavillo Historical Museum on Thursday, May 26th. Advance registration is required; call the Osborne Nature Center to grab a spot. The shuttle will leave from Osborne at 10:30 AM for an exciting investigation into "the Gem of the Prairie."

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