Penstemon Mitchell, a genus of highly divergent plants, is increasing in popularity, as documented by the number of newly released Penstemon cultivars and the number of recently published books on Penstemon (Lindgren and Wilde, 2003; Nold, 1999; Way and James, 1998). Many Penstemon crosses and hybrids have been reported (Lindgren, 2006). However, summarizing the breeding and hybridization in the genus Penstemon can be confusing because of incomplete or lost breeding records and the failure to register new Penstemon cultivar names with the appropriate authority (Lindgren, 1993). In addition, the correct parentage of “natural hybrids” is rarely known with certainty.
Interspecific hybrids offer the opportunity to expand the choice of plants available in any one genus. They can extend the flowering season, offer novel flower colors, expand the range of disease tolerance, generate new combinations of useful traits, and offer additional germplasm for adaptation to soil, climate, and moisture extremes. Cronquist et al. (1984) indicate that cross-breeding experiments could lead to reorganization in species classification in the genus Penstemon. Penstemon hybrids may also be valuable in determining evolutionary relationships in this genus (Wolfe et al., 2006). Bridging, during which one hybrid enables the breakdown of genetic barriers to incorporate other species into a Penstemon breeding complex, demonstrates the potential value Penstemon hybrids can have (Viehmeyer, 1958).
An initial summary of Penstemon hybridization, based on a standard Penstemon classification system, has been reviewed by Lindgren (2000). This summary discussed six general classes: 1) Dasanthera (Raf.) Penn. subgenus hybrids, 2) Penstemon Mitchell section hybrids, 3) Peltanthera Keck section hybrids, 4) Flathead Lake hybrids, 5) Gloxinoide-type hybrids, and 6) miscellaneous hybrids. Several other summaries relating to Penstemon hybrids have been published (Moore, 1980; Vesall, 1990; Viehmeyer, 1958).
Way and James (1998) discussed and summarized many of the European Penstemon hybrids. Species parents most often mentioned for the European hybrids include P. hartwegii Benth., P. gentianoides (Humboldt, Bonpland & Kunth) Poiret, P. kunthii G. Don, P. campanulatus (Cav.) Willd., P. isophyllus Robinson, and P. cobaea Nutt.
At the University of Nebraska–Lincoln (UNL) West Central Research and Extension Center (WCREC), a significant number of crosses/pollinations have been made in the genus Penstemon since the breeding and selection project was initiated. These include crosses between plants of different species, crosses between pure species and hybrids, and crosses between hybrids and other hybrids. The objective of this report is to summarize the interspecific crosses in the genus Penstemon at the UNL WCREC over 10 years, 1996–2005, and compare those results to other reports in the literature. The majority of species used in the crosses at the UNL WCREC have some adaptation to the high plains area of the Midwest United States and are, in general, assigned to a relatively few subsections. Species not well adapted to Nebraska were, in most cases, not used because of their low adaptability to Midwest growing conditions (e.g., low temperature, soil pH, drought). Crosses were made to maximize the production of potentially new ornamental plants, not to develop a systematic method to evaluate crossability across taxonomic units. This approach led to a disproportionate large number of pollinations in some crossing groups and few in other crossing groups.
Species in the genus Penstemon can be grouped according to subgenera, sections, and subsections (Table 1). There are six subgenera, 13 sections, and 22 subsections in the genus (Lindgren and Wilde, 2003; Lodewick and Lodewick, 1999). Some subgenera are not divided into sections and not all sections are divided into subsections. Two subgenera, Cryptostemon and Dissecti, are monotypic (Wolfe et al., 2006).
Cronquist, A., Holmgren, A.H., Holmgren, N.H., Reveal, J.L. & Holmgren, P.K. 1984 Intermountain flora: Vascular plants of the intermountain West, USA Vol. 4 New York Botanical Garden Bronx, N.Y
Lindgren, D. 2006 List and description of named cultivars in the genus Penstemon. University of Nebraska Coop. Ext. EC1255 Univ. of Chicago Press Chicago
Lindgren, D. & Wilde, E. 2003 Growing Penstemons: Species, cultivars and hybrids. Amer. Penstemon Soc InfinityPublishing.com Haverford, Pa
Lodewick, K. & Lodewick, R. 1999 Key to the genus Penstemon and its related genera in the tribe Cheloneae (Scrophulariaceae) K. Lodewick Eugene, Ore
Wolfe, A.D., Randle, C.R., Datwyler, S.L., Morawetz, J.J., Arguedas, N. & Diaz, J. 2006 Phylogeny, taxonomic affinities, and biogeography of Penstemon (Plantaginaceae) based on ITS and CPDNA sequence data Amer. J. Bot. 93 1699 1713