Stem Hairs in the Hedeoma drummondii complex
by Bob Harms
R. Irving's 1980 (Sida 8:257-9) article describes stem vestiture for the H. drummondii complex taxa as:
This page is presented to give a somewhat clearer sense of the stem hairs, but only for the spring—early fall stem growth. Winter dimorphism (beginning with shoots at the end of September) gives much denser pubescence with longer and morphologically different trichomes — these are shown on a separate page. What the images below show are:
- H. d.
- densely pubescent or puberulent above with the hairs tightly retrorsely curling, glabrate below.
- H. r. r.
- densely pubescence [sic], nearly canescent above with tightly retrorsely curling hairs, glabrous below.
- H. r. s.
- densely pubescent above with retrorsely curling hairs, puberulent below.
- pubescence of light to moderate density;
- great variation in trichome length; the shortest with H. drummondii and longest with H. r. var reverchonii, but with overlap among the 3 taxa;
- all trichomes are retrorsely curved, with the distal trichome cell often bent downward (thus 'curling') — I assume 'tightly curling' describes hairs bent close to the stem surface;
H. drummondii trichome
- differences in upper/lower stem position were not found (other than those resulting from age and tendency for the trichomes to break apart above the base); but differences in both density and length on the two sides of stem nodes were common;
- neither canescense nor puberulence was noted on spring—summer stems, but did occur with winter dimorphism.
(5-unit scales are 5 mm. Several images are clickable.)
H. reverchonii var. serpyllifolia
H. reverchonii var. reverchonii
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