Hiking in the Cascade mountain range in WA, I found both a very long-inflorescence and stout yellow mustard family plant (Brassicaceae) I'd never seen before. I narrowed it down to 1 of 2 wallflower species of the genus Erysimum. But... which one is it?! How do these Erysimum species differ?
One big clue- the old Flora of PNW text only has 1 of the species while newer lists (shout out to Burke Herbarium, my plant-porn go-to) distinguish two very similar species. So these must have recently been teased apart from formerly being both under Erysimum arenicola. I found that most likely both the forms I found (one in moister milder lower elevation habitat and the other in more open rockier higher elevation) are both E. capitatum. But... why/how?
And what are the other Erysimum "wallflower" species like? Cute bright yellow-orange mustardy guys, all of em. Some are native, some are introduced, some very widespread in WA, some very isolated patches.
Here's my Botany Hack for Erysimum species:
In the table below are the 6 Washington species of Erysimum with their general characteristics and bold ones being most useful to distinguish between species. The plants I found were clearly native to the area and also most similar to either E. capitatum or E. arenicola.
The main difference between the closes 2 species was in their seed pods which are long single-side row silique fruit made from 2 fused carpels common to the mustard family, and in their petal size. The leaves overlapped in size and shape, and clearly vary by their habitat characteristics- water, shade, soil, etc.
After looking closely at my photos I decided both these forms were the newer species- Erysimum capitatum with the fatter fruits and larger flower petals. Always try to get photos of the leaves and flower details, especially any fruits if present which can really help ID these big genera with species having highly overlapping traits. There are a lot of yellow Brassicaceae species!
As you can see, the leaves vary from folded purplish and gently dentate, to fairly flat green and sparsely tiny-tooted. And from short to tall, green to purple stems. Plants don't make it easy on us botanists, which is part of the fun.
Adding this new plant friend to my notebook of species observations on hikes. Maybe someday I'll know the name of every plant in a given area. Good to have goals!
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