Leaf Trichomes

H. reverchonii var. reverchonii stem & leaf/petiole trichomes
7 April 2013, Hays. Co.

Leaf & Petiole Trichomes in the Hedeoma drummondii Complex

by Bob Harms email-here

R. Irving's 1980 (Sida 8:257-9) article describes leaf vestiture for the H. drummondii complex taxa as:

H. d.: leaves ... glabrous or sparsely pubescent above, densely pubescent below
H. r. r.: sparsely pubescent above, densely so below and on the margins
H. r. s.: glabrate above, densely pubescent below

In sharp contrast with stems (and pedicels), leaves & petioles have antrorsely directed trichomes. Trichome lengths on leaf margins seemed slightly smaller than with stems, but overall the same differences were found as with stems, with those H. drummondii shortest, and slightly thicker, and bent more sharply. Upper leaf pubescence is clearly different, as was noted by Irving (above). The trichomes of the upper surface are much thinner as well as sparser in comparison with those of the lower surface; and being translucent made them difficult to image. [Imaging also creates a false impression of greater density on the margins.] The greatest difference is with H. drummondii, where I had difficulty finding any hairs at all. I found no significant difference in this regard between H. r. s. and H. r. r.

Petiole trichomes are similar to those on the leaf margins, with an abrupt antrorse orientation at the stem.

The markedly different leaf hairs in fall/winter are presented on a separate page.