Rare Plant Pops Up From Nowhere - Short Green Milkweed

A curious story.

Somme Prairie Grove has harbored one individual of this rare milkweed for decades. Normally, we would have paid more attention to such a plant. 

But we mostly forgot about it, because it seemed like a mistake. It's a plant of specialized habitats - dry prairie or sand areas. We have no dry prairie or sand at Somme. 

We did keep an eye on it, as sort of a curiosity. Year after year one or a few stems emerged - connected underground - all one plant. The other vegetation near it was initially short, old pasture plants, mostly poverty oats, Canada bluegrass, and daisy. 

It was not our goal to focus especially on rare species, especially rare species not part of this community. We were trying to restore a natural prairie ecosystem. Our major historic source, H.S.Pepoon's Flora of the Chicago Region (1920) gives this region's habitats for short green milkweed only as "sand dunes" of Indiana and "the Waukegan moorland" - today Illinois Beach - another sand habitat. We continued to mostly ignore it. 

One year Jim Steffen from the Chicago Botanic Garden came by to compare notes on our parallel experiments. When I pointed out the curious milkweed, he recommended that we plant another; that was the only way it would make seed and increase its numbers; he could give us a plant raised from seed gathered not too far away, and not from sand but from a gravelly moraine. Could it be legitimate here? We accepted the gift, planted it in a sunnier area, and it died, or at least we never saw it again. 

Over the years, with fire and the restoration of seed, the vegetation around the original plant grew thicker and more competitive, and the number of stems decreased. Some years a cursory search revealed none, though it may have produced only a few leaves, and we may have looked in the wrong places. Milkweeds are big travelers, at least over short distances. They move by roots, underground, sending rhizomes many feet to explore possibilities, putting up stems in various spots from year to year. 

Eriko Kojima frequently gathers rare seed in the area of this milkweed. The prairie vegetation here has been growing increasingly impressive (prairie coreopsis, white and purple prairie clovers, prairie gentian, prairie lily, Leiberg's panic grass, prairie dropseed, and others). And as nearby trees grew, the area was increasingly in semi-shade and harbored Seneca snakeroot, New Jersey tea, Maryland sanicle, and meadow parsnip (Thaspium trifoliatum) - savanna plants that thrive in dappled shade. We especially wanted seed from that group because, belatedly, we'd figured out that Somme Prairie Grove was indeed originally mostly savanna rather than prairie. All prairie plants also grow in savannas, but many of the non-prairie savanna plants are especially hard to find.   

This June while harvesting Seneca snakeroot, Eriko noticed that two stems of the short green milkweed had emerged, one about ten feet farther out into full sun. Interesting. We still mostly forgot about it.

But our slumbering interest was awakened dramatically when we noticed the plant below, a quarter-mile away in the area called Middle Slope:

Hiding behind a leadplant are two stems and three flower umbels of the short green milkweed.
Where did they come from?  

We've identified 486 species of native plants at Somme Prairie Grove. Perhaps we can be forgiven for not keeping up to date on every one. But this new find prompted us to review the latest info in Wilhelm and Rericha (Flora of the Chicago Region, 2017). The habitats they list for short green milkweed are not limited to sand but include gravelly savannas. Somme is on the Lake Border Moraine; indeed it includes some gravelly areas. Short green milkweed reasonably belongs here. Has this "new" plant been lurking, unseen until now, throughout our 43 years of stewardship? Especially if not flowering, the plant would be easy to miss. Even in glorious full bloom, its green flowers hardly pop. Or is it new? Could Jim Steffen's plant have produced flowers and seeds, and one blew to Middle Slope? Or is it even possible that some green milkweed seed from miles to the west, like at Shoe Factory Road Nature Preserve where there are quite a few green milkweeds on a dry gravel hill, blew miraculously in a collaborative wind all this way? Very unlikely. But possible. 

We'll never know how it got there ... and really don't care all that much. We're about biodiversity conservation. A potentially reproducing short green milkweed population is now on the team.