HEDR-HP-det-31Oct13-7in.jpg HEDR-HP-det-4Dec13-4in.jpg
October 31 Winter leaves — December 4
H. drummondii (click image to enlarge)

Vestiture in the Hedeoma drummondii Complex
by Bob Harms  email-here

Nearly all plant surfaces in the Hedeoma drummondii complex are evenly covered with multicelular uniseriate trichomes, but these hairs vary a great deal depending upon their location, and even upon the seasonal ontogeny of the plant. (Contrast the October and December stem partials of H. drummondii above.) In the images below eight distinct anatomical areas are labeled A—H.

A—C — hairs are retrorsely bent or curled
A: stem, B: peduncle (not visible for H. reverchonii var. serpyllifolia), C: pedicel
D—F — hairs are antrorsely bent or curled
D: petiole, E: leaf surface (upper surface may lack hairs), F: bracteole
G — hairs short & erect, spreading
outer corolla tube
H — proximal hairs retrorsely curved; distal hairs antrorsely curved; spreading hairs generally occur at a point in between, that point varying by taxon
calyx tube
Treated elsewhere are the highly complex hair structure of the calyx, seasonal differences, and the corolla tube.

[Click on image for enlargement.]

H. reverchonii var. reverchonii
HEDR-HP-11May-w_key-24C-6in.jpg HESE5-11May-hairdet-24C-6in.jpg
H. drummondii H. reverchonii var. serpyllifolia
The image below left (click to enlarge) shows the interplay of retrorse (A,C) & antrorse (D, E) hairs at a stem node; below right the structure of the stem hairs is shown to result from rather angular bending at the cell septa.

This pattern is shared by all 3 taxa. One must wonder what is going on here. I would speculate that the trichome orientation impedes insect access to the axillary shoot meristem and the ovary at the base of the calyx. Trichomes of the stem and pedicel are directed down against insects ascending from below. Those of the leaf (including bracteole) and petiole are directed upward (as are the upper calyx trichomes) against insects alighting on the leaves. Possibly more substantial protective mechanisms are the dense annuli within the calyx and the corolla tubes, as well as the calyx teeth.

H. drummondii trichomes (left: 20x; right: 40x)

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