Lactuca....hirsuta?

Lactuca hirsuta is one of the most under detected species of vascular plants in the Midwest. There I said it. It is completely off the radar for most folks, yet I see it with considerable frequency, at least here in the Ozarks. The USDA Plants website shows that it occurs in most every state northeast of Texas (north to MN and east to Maine and GA) yet it is listed from shockingly few counties in these states. I don’t know how this creature has escaped detection. Perhaps its anomalous distribution stems for the common precept that Lactuca canadensis can be distinguished from other Lactuca by the salmon/orange sap color. While this it true, one must then distinguish Lactuca hirsuta which also possesses this quality. This is easily done since L. hirsuta, as the name implies, is hirsute and L. canadensis is glabrous (disclaimer: some specimens of L. canadensis can be very slightly pubescent and some L. hirsuta can be sparsely pubescent but the vast majority are clear-cut).

Here is quick shot of the stem and leaves of L. hirsuta (above). And for comparison, here is a shot of the stem and leaves of L. canadensis (below). Also notice the difference in overall leaf shape between the two species.

There are other subtle but taxonomically satisfying characters. Most notably, the leaves of L. hirsuta are progressively shorter toward the top of the stem while those of L. canadensis remain roughly the same length from tip to toe. Also, the involucres of L. hirsuta are range from 15-22mm long where those of L. canadensis are typically 10-14mm long.

Lactuca hirsuta (above)
Lactuca canadensis (below); my thumb nail is 15mm long, for scale.

Esteemed Missouri botanist Alan Brant pointed out to me that the inflorescence (branches and involucres) of L. hirsuta are often infused with a dark purple coloration while those of L. canadensis are mostly green with some hits of purple here and there. That can clearly be seen in the involucre photos above.

So, as Lactuca are bolting and blooming across eastern North American, in your travels, keep an eye out for the lonely but hairy L. hirsuta. While I don’t have a great grasp on its habitat requirements (perhaps a bit more conservative than L. canadensis), it seems to prefer dry acidic soils with just a touch of disturbance suffused with a sparkle of full sun. Rocky soils with sparse vegetation that have recently witness fire are ideal. I remember seeing it at Indiana Dunes National Lakeshore. I can imagine that open sand would suit it just fine. Another place to find it would be the neglected stacks of almost any herbarium in eastern North America, where it has undoubtedly been misidentified as L. canadensis. Hey, let’s print off some annotation labels and head to the herbarium!

Comments

  1. Hey Justin. I can guarantee that I've never seen L. hirsuta and confused it with L. canadensis. Everything I've ever called L. canadensis has been completely glabrous. I think I would confuse L. hirsuta vegetatively with L. biennis, based on the leaf shape, before confusing it with L. hirsuta; however, L. biennis would have white sap. Regardless, I'll keep an eye out for L. hirsuta as well.

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  2. Yeah, I failed to mention that the basal rosettes of L. hirsuta, which are seen more often than flowering plants, have leaves shaped just like those of L. canadensis. In fact, unless you bend down and feel the leaf for hairs, there is no way of knowing. I remember seeing it at a few places in the Indiana Dunes area, so it is definately around your neck of the woods. Were you there when we taught it to the folks at the INDU workshop?

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  3. I wasn't there when you taught it. It's known from Porter County, just west of Michigan City, as well as from Berrien County, Michigan.

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  4. So...

    In Wisconsin last week, I think I saw L. hirsuta. There were hairs on the midrib, and it had an orange sap. Think that's what it was?

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  5. Maybe. Lactuca canadensis can have hairs on the midrib. You need hairs on the abaxial and adaxial leaf surfaces.

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  6. Way past the time limit on this post, but I think it worth noting the beautiful fall color of this species. Almost brass-colored, both stems and seeds. Saw this in seed in the Irish Wilderness and at Lower Rock Creek after Thanksgiving, after having previously ID on a MONPS trip. The fall color alone should make location of new colonies easier.

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  7. Awesome! I've never seen it so late in the year. I'll keep an eye out for it next fall.

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