2013-08-01

Artemisia leaf variation

I've been pondering on Artemisia.  I believe the picture below is Artemisia, A. douglasiana (Mugwort, California Mugwort, Douglas' sagewort) if I'm not mistaken. I took it while on a recent hike in Barton Flats.  But the leaf shapes are so very different!
Artemisia douglasiana
Artemisia grows by rhizomes, and these two appeared at the edge of a large patch.  One would expect a plant that grows by rhizomes to be genetically identical across the entire patch.  Yet I noted similar leaf variation in Artemisia I found at nearby Camp Tahquitz.  So what leads to this observed leaf variation? 

My naive ideas:
Older leaves develop the lobed character.  Young leaves don't have it.
These are actually genetically distinct plants and the lobed leaves are highly variable.
Lobed character is dependent upon the growing conditions (unlikely, since these are so close together)
These aren't both Artemisia. (always a possibility, but unlikely since the lower leaves on both plants are lobed)

Variability in the leaf is indicated in the Calflora database too, both in photos and in their link to the Jepson manual treatment, which seems to allow for 3 to 5 or more lobes: "Leaf: evenly spaced, 1–11(15) cm, narrowly elliptic to widely oblanceolate, entire or coarsely 3–5(+)-lobed near tip, ± sparsely tomentose adaxially, densely white-tomentose abaxially."

There's some new vocabuluary for me there, so here's a translation:

"Leaf: evenly spaced, 1–11(15) cm, narrowly elliptic to widely oblanceolate [pointed more narrowly at the stem end], entire or coarsely 3–5(+)-lobed near tip, ± sparsely tomentose [matted hairs] adaxially [stem-facing, esp on top of leaf], densely white-tomentose abaxially [away from stem facing, esp on bottom of leaf]."

I actually own a bound copy of Jepson, purchased against the day that I might have to resort to it.  I guess that day has come. Still, the single pointed leaf isn't explicitly called out in Jepson.  In the photo you can see that the lower leaves of both plants are lobed.

So, does anyone know why the leaves in this photo look so different?

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