Hybridization of Penstemon Barbatus (Scrophulariaceae) of Section Elmigera with Species of a Section Habroanthus

Abstract

Hybridization between Penstemon barbatus (Section Elmigera Benth.) and various species of Section Habroanthus Keck is not uncommon. Reports of hybrids of P. barbatus with P. virgatus A. Gray, P. glaber Pursh, P. comarrhenus A. Gray, and P. strictus Benth. are summarized. Hybridization between P. barbatus and P. strictus is reported. None of the hybrids are given Latin names. The purpose of this paper is to bring together several scattered re- ports of hybridization between Penstemon barbatus (Cay.) Roth of Section Elmigera and species of Section Habroanthus. A deeper pur- pose is to indicate a close genetic relationship between the two sections and finally to suggest an origin of P. barbatus ssp. trichander (A. Gray) Keck, which combines characters of both sections. Section Elmigera is composed of some half-dozen or fewer species, all of which have red-tubular flowers that are pollinated by humming- birds. Section Habroanthus contains about 4 times as many species, all of which have blue ventricose flowers that are pollinated by hymen- opterous insects. (Some doubt does exist, however, whether a species such as P. parvus Pennell, which has less ventricose and straighter corollas, is actually pollinated by hymenoptera.) Anther dehiscence is very similar in the two sections and this character alone tends to separate these sections from all others of the genus, although many less tangible characters do also. Since the obvious differences between the two sections are flower-color and -shape, and since these are adap- tations for different types of pollinators (Straw, 1956), it might be of interest to review the putative cases of hybridization of one hum- mingbird-pollinated species (P. barbatus) with insect-pollinated species: