Hedeoma drummondii Click to enlarge. These scans and those below are from TEX/LL specimens determined by R.S. Irving

by Bob Harms 

Key in R.S. Irving 1980, The systematics of Hedeoma (Labiatae), Sida 8: pp, 234, 258:
Characters with significant overlapp for H. drummondii & H. reverchonii var. serpyllifolia are highlighted in red.

11. Plants annuals or herbaceous perennials, occasionally somewhat woody at the base, averaging less than 25.0 cm in height; leaves bright green, over three times longer than wide; calyx weakly hirsute, the upper and lower teeth usually strongly convergent; corolla 7.0–11.0 mm long; widespread; odor of peppermint.
[in text Calyx finely hirsute, 5.0—6.0 mm (5.6 mm) long]

… H. drummondii

11. Plants suffruticose typically averaging over 25.0 cm in height; leaves gray or dark green, usually less than three times longer then wide; calyx coarsely hirsute or hoary villous, the upper and lower teeth incompletely closing the orifice; corolla 8.0—15.0 mm long; west and central Texas to south–central Oklahoma; odor of camphor or lemon.

… H. reverchonii

Hedeoma reverchonii var. reverchonii Click to enlarge

then for H. reverchonii:

1. Plants 25.0—60.0 cm tall branching usually restricted to the base and the upper l/2 of the shoots; leaves gray green, ca 3.7 mm wide, 11.7 mm long; calyx 6.0—7.0 mm long, very coarsely hirsute to hoary pilose; the upper teeth widely spreading; corolla large, 10.0—15.0 mm long, the tube conspicuously dilated upwardly; plants restricted to the eastern edge of the Edwards Plateau and Lampasas Cut Plain of central Texas, and south central Oklahoma; lemon–scented in typical forms.

… l8a. H.r. var. reverchonii

Hedeoma reverchonii var. serpyllifolia Click to enlarge

1. Plants 15.0—40.0 cm tall branching freely along the lower 2/3 of the shoots; leaves dark green, ca 3.0 mm wide, 8.3 mm long; calyx 5.0—6.0 mm long, coarsely hirsute, the upper teeth erect or only slightly spreading laterally; corolla small, 8.0—10.0 mm long, the tube only very slightly dilated upwardly; plants from eastern edge of Edwards Plateau south co the Central Coastal Plain of Texas and west to southeastern New Mexico; camphor–scented.

… 18b. H.r. var. serpyllifolium

[sic., should be var. serpyllifolia; hedeoma is feminine.]