Phacelia crenulata cf P. integerifolia

There's Phacelia coming up all over the place around here right now, and I've been thinking it's mostly P. crenulata, but P. integerifolia is also a possibility. So I chatted with @aspidoscelis about the vegetative characteristics that distinguish them. He had some very useful guidance that I'm leaving here for future reference. Note on taxonomy: P. corrugata has been treated with both species rank and as a variety of P. crenulata.

Phacelia crenulata & Phacelia corrugata: basal leaves usually flat against the ground (at least the older basal leaves; harder to tell after those have senesced, or in more shaded plants. Phacelia integrifolia: usually all basal leaves angled upward at something like 20-30° or more.

Depth of leaf lobing: shallowest in Phacelia integrifolia, deepest in Phacelia corrugata.

Ratio of leaf length to leaf width: highest in Phacelia crenulata, lowest in Phacelia integrifolia. Leaves of the Four Cornersy Phacelia integrifolia on iNat seem to be narrower than I’m used to, so the difference seems to be less pronounced.

Prominence of teeth on the margins of the lobes: lowest in Phacelia integrifolia, highest in Phacelia corrugata.

Also, Phacelia integrifolia is mostly (but of course not always) associated with sandy soils, at least until you get over to Phacelia integrifolia var. texana. Phacelia crenulata seems to like loamier stuff. I’m not sure what Phacelia corrugata does in this regard.

When flowering, you can also use anthers; those of Phacelia crenulata are yellow, those of Phacelia integrifolia are dark purplish (at least externally).

Having looked at a bunch of iNaturalist observations of Phacelia with those dimensions in mind, the distinction between P. crenulata and P. integerifolia now seems pretty clear based on leaf morphology in many (but not all) cases.

Flora of the Four Corners Region (Heil et al. 2013) says that Phacelia crenulata in the area of the San Juan River drainage covered by the Flora are all var. corrugata, though it seems likely that var. crenulata would also be here.

Posted on April 6, 2023 08:20 PM by crediblecorvid