Flora of North America species comparison

Variety lasiophylla occurs over most of the range of the species in Louisiana and Texas; var. pycnostachya occurs in the northern counties of those states and, apparently, also sporadically southward through the range of var. lasiophylla, at least in Texas, where it grows in drier habitats than var. lasiophylla. In Louisiana and Texas, var. pycnostachya begins flowering in mid-June and continues through July (through August more northward in its range), usually well before the main flowering period of var. lasiophylla. Despite these indications of reproductive isolation, apparent intermediates are commonly encountered (usually these are plants with dense cauline vestiture but sparsely pubescent to glabrate leaves, compared to the densely piloso-puberulent stems and leaves of typical var. lasiophylla). Most of the plants with reduced vestiture in the range of var. lasiophylla also have the later flowering period.

In Pearl River and Hancock counties, Mississippi, and St. Tammany and Washington parishes, Louisiana, plants with vestiture of var. lasiophylla have phyllaries with rounded to slightly acute apices, different from the rest of the species. These were named Liatris serotina, and it seems likely that they originated as hybrids between var. lasiophylla and L. spicata var. resinosa, whose ranges meet in that area. Some plants of L. spicata in Illinois, Indiana, and Minnesota also develop cauline vestiture; the tendency apparently is evolutionarily independent of that in var. lasiophylla.

(Discussion copyrighted by Flora of North America; reprinted with permission.)