H. drummondii, 11 May 2013 [Travis Co.].

Corolla Trichomes in the Hedeoma drummondii complex
by Bob Harms  email-here

R. Irving's 1980 (Sida 8:257-9) article give the following description of corolla vestiture for the H. drummondii complex taxa:

H. d.
sparsely pubescent in the throat, densely1 so below forming an annulus
H. r. r.
sparsely pubescent in the throat, densely1 so in the tube forming a well–defined annulus
H. r. s.
sparsely pubescent in the throat, densely1 so below forming an annulus
1In general I do not share Irving's vague use of the term dense in his descriptions of vestiture. Dense is not a clearly defined botanical term, but I would expect it to reflect crowding, with little space between hairs, obscuring the surface below — which is only sometimes appropriate where he uses the term.

H. reverchonii var. reverchonii [Travis Co.]. (photographed at 100x)

Nowhere in his general treatment of Hedeoma does Irving describe the vestiture of the outer corolla surface, which in the H. drummondii complex is (1) evenly covered with short (0.05—0.15 mm), slightly curved or relatively straight at 90° from the surface & thin hairs (multicellar but with an extremely thin terminal cell, often over half the length of the trichome), unlike the hairs on other parts of the plant, and (2) unlike the corolla hairs of most other Texas Hedeoma taxa (of those for which specimens were available at TEX — i.e., H. acinoides, H. apiculata, H. costata, H. hispida, H. mollis, H. nana, H. plicata). With exception of the short annulus at the base of the tube and scattered hairs in the throat, the inner surface of the corolla is glabrous. Within the H. drummondii complex I found only small differences in trichome size (shortest hairs with H. drummondii).

H. r. r., corolla tube. Note that hairs extend into the calyx tube, almost to the bottom, where they gradually reduce in length, and disappear at roughly the area below the annulus in the tube.


H. d.
H. r. r.
H. r. s.
H. r. s.

Scattered Hairs in the Throat

These hairs are approximately the same type and size as those on the outer surface. Most do not show well on the smaller images of this page, so you will need to click for enlargements.

H. d.
H. r. r.
H. r. s.

The Annulus at the Base of the Corolla Tube


H. d. corolla tube dissected to show the annulus (yellow box ‘A’), a ring of hairs ca. 0.6 mm long
ca. 1 mm from the base of the tube. The style in the tube is marked ‘B’.

Corolla annulus hairs are similar in form to those on the outer surface of the corolla, but generally less dense. Dissecting the corolla to examine the annulus does not produce good images. By contrast the calyx annulus is striking, with long and tightly packed trichomes, often in two series.


H. d.
H. r. r.
H. r. s.

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