H. reverchonii var. reverchonii — H. r. var. serpyllifolia — H. drummondii

by Bob Harms 

A detailed study of the Hedeoma drummondii complex in Central Texas (i.e., H. drummondii, H. reverchonii var. reverchonii, and H. reverchonii var. serpyllifolia, using more recent names) was presented by Robert S. Irving in his 1968 U. Texas at Austin dissertation. Irving's dissertation actually treated this complex as a single species, and expressed difficulty in determining individual herbarium specimens (p. 141):

In treating the H. drummondii complex as a single species divided into 2 subspecies, each grouping 2 varieties, it should not be surmised that the taxa are clearly defined morphologically; rather, each variety is no more than a "catchall" for a host of interrelated elements or races. Despite intravarietal variation, I have, using herbarium material, been unable to distinguish, with any degree of certainty, among any of the sub-varietal units.

• Robert Irving's 1980 Key for the H. drummondii Complex

• Scent–producing Volatile Terpenoid Components as Primary Differentia

• The BRIT 1999 Key

• Color as Not Reliable

• Calyx Morphology as a Rich Source of Differentiae

• Vestiture in the H. drummondii Complex

• Stem Vestiture

• Pedicel Vestiture

• Peduncle Vestiture

• Leaf/Petiole Vestiture

• Bracteole Vestiture

• Corolla Vestiture

• Vestiture with Other Texas Taxa

• Hedeoma mollis Vestiture

• Hedeoma mollis Branching Trichomes

• Differentiae Based on Seasonal Morphology

• Seasonal Leaf/Stem Dimorphism as Differentia

• October 2012 Collections of the Three Central Texas Hedeoma Taxa

• Pubescence of Winter Stems

• Pubescence of Winter Leaves

• Winter Greenhouse Plants: H. drummondii & H. reverchonii var. serpyllifolia

• Mid-to-late March

• Late March/Early April

• Calyx Trichome Length

• Cleistogamy vs. Chasmogamy

• Seedling Leaves

• Hybridization & Variation

• Scent with Hybrids

• Evidence that H. reverchonii var. serpyllifolia is a Stable Taxon