Jacob’s Ladder

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Filed under Outdoor Notes

May 13, 2010

Polemonium reptans

Jacob's Ladder

This is a Jacob’s Ladder. The question is, which one?

Unhappily, many of our native plants are difficult to tell apart at the species level, as is the case with our three species of Jacob’s Ladder (Polemonium). The silver lining to that black cloud is that it provided me with an excuse to buy Rhoads and Block’s encyclopedic Plants of Pennsylvania.

What an amazing book; what an astonishing accomplishment. If you have a serious interest in the vascular plants of our area, you should buy this book.

Like any definitive guide to identifying plants or animals down to the species level, Plants of Pennsylvania uses keys. Now, for brevity’s sake, the keys rely on botanical terminology—where one word, e.g. “hypanthium,” can stand for a long definition: “cup-like floral structure resulting from the fusion of the calyx, corolla, and stamens, often surrounding or partly fused to the ovary(s).”

You can see that repeating that every time a cup-like floral structure, etc. came up would make for a very long book, and given that the book is already 1042 pages long, brevity is a good thing. Yes, all this jargon can make it a little tough on the layperson. Fear not, however, there is an excellent glossary; moreover, the keys are extensively supported with outstanding illustrations by Anna Anisko.

Close up of Jacob's Ladder

Close up: Jacob's Ladder

Back to our Jacob’s Ladder. The key factor for telling our three species of Polemonium comes down to whether or not the male parts of the flowers, the stamens, stick out beyond the petals—collectively, the corolla. Well, they don’t. Only the style—the little curly looking thread—extends beyond the corolla; so that eliminates the rare P. van-bruntiae.

Now, is the pedicel (the little stalk of the individual flower) as long as or shorter than the calyx (the greenish part that links the pedicel to the corolla)? In P. caeruleum the pedicel is shorter than the calyx; in P. reptans, it is as long.

Actually, to me, the pedicel appears even longer than the calyx; so, by process of elimination, I’m going with P. reptans—Spreading Jacob’s Ladder.

But I could be wrong.

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