Warning: more than typical amount of plant geekery follows.

my trusty D3200 poised by some bluets

As you may recall from yesterday, I went to the C&O Canal to determine if there were indeed two different species of bluets (Houstonia) in the area.

After 15 minutes of walking I arrived at the stand in question, and took a close look.  A really close look.  And lots of pictures.  What I found:

Two plants, one with five flowering stems, one with three flowering stems.  All were about seven inches tall.

The uppermost stem leaves were narrow and one-veined.

The middle and lower stem leaves were oval and three- or five-veined.

It seems this species is Houstonia purpurea.

I walked another 50 yards or so, knowing that there was another stand somewhere, but I couldn’t find it, so I went back to the first stand and studied it a little more. Kneeling on the towpath and looking around me, I spotted some other flowers that I’d missed while standing.

This was about eight feet away from the first stand.  It’s a single plant with six flowering stems, all about seven inches tall (just like the first stand).

Look how long and narrow the leaves are compared to the other plant.  This one is H. longifolia.  I think.  Note the pair of leaves at top and bottom of the picture; they’re a little more oval and rounded at the base.  Could this be an intermediate form?!

the flowers of H. purpurea…

…are almost identical to the flowers of H. longifolia

Both Venus’ pride (H. purpurea) and longleaf bluets (H. longifolia) can be found across most of the eastern and mid-west US, with the latter species ranging further north and west into Canada. Longleaf bluets are endangered in Connecticut and Massachusetts, of special concern in Maine, and historical in Rhode Island.

Houstonia species
Rubiaceae

From mid-April to mid-May, the dryer, rocky soils around Carderock will be carpeted in rattlesnake weed and this adorable plant [left].  Standing only a few inches high, each stem bearing a single, terminal flower and few or no leaves, it’s very easy to identify as Houstonia caerulea (azure bluets).

Half a mile or so west on the C&O Canal towpath, come early June, you might see just a dozen or so of these plants [right] on a certain dry hillside.  Standing about a foot to a foot and a half tall, with a small terminal cluster of flowers and three-nerved, oval leaves, it’s pretty easy to tell that this one is Houstonia purpurea, variously known as large bluets, woodland bluets, and Venus’ pride.

Here’s when I get into trouble. Satisfied with the identification, I fail to examine every single plant and start concentrating on taking lovely photos, until I get one that I really like.

<—– Like this one.

Yesterday, I posted that photo to an internet discussion group and was quickly challenged: isn’t this Houstonia longifolia (long-leaf bluets)?  Let’s consider it, with descriptions from my three favorite ID books.*

H. purpurea: stem leaves egg-shaped or broadly lance-shaped, with 3-5 veins (Newcomb); plants erect, 6-20″, leaves rounded or notched at the base, stalked or stalkless (C&G); leaves oval, paired, sessile, entire, 3-veined (Peterson).

H. longifolia: stem leaves lance-shaped or oblong, 1-veined (Newcomb); plants erect, 4-10″, leaves narrowly oval or narrowly oblong, 1-nerved, tapering to base, stalkless (C&G); a small plant, slender paired leaves (Peterson).

Note that I didn’t describe the flowers; in all three sources the descriptions pretty much match, but more importantly, there can be a lot of morphological variation in flowers.  Color is probably the worst clue, because it can vary so much.  And look at the previous picture again: can you see that the topmost flower has 5 petals, while the others have 4?  These things happen.  To distinguish these two species, you need to examine the leaves.

Back to the question: which species is pictured?  There isn’t enough information to say for sure. Only the uppermost stem leaves are shown clearly, and while they appear to be narrow and 1-veined, the same can be said of the uppermost stem leaves on the plants ID’d as H. purpurea (in other pictures; I’ll spare you). Is it possible there are two different species in a single stand of plants?  Sure. Is it likely?  I don’t know enough to say.

These things bother me.  As I finish my third cup of coffee, I’m going to hit “publish immediately”, get my camera out, and go to the canal.  If I’m lucky these plants will still be blooming and I’ll get a good look.  If they aren’t, I probably won’t be able to pick them out from all the other foliage in the area.

I’ll post an update later today.

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*Newcomb’s Wildflower Guide; Wildflowers in the Field and Forest (Clemants and Gracie); Peterson’s Field Guide Wildflowers Northeastern/North-central North America