Except for Thermopsis barbata Benth. ex Royle, which produces reddish-purple flowers, all species in Thermopsis have yellow flowers (Chen et al., 1994; Wu and Raven, 1994). Flower color in Baptisia ranges from white to yellow to blue (Larisey, 1940). In both Baptisia and Thermopsis, perfect flowers with superior ovaries are borne on terminal racemes, though some Baptisia species produce flowers that occur individually in leaf axils (Chen et al., 1994; Larisey, 1940). Seed pods of Baptisia are inflated while those of Thermopsis are compressed (Chen et al., 1994). Although polyploidy is wide-spread in the Fabaceae, no polyploids have been found in Baptisia and only two polyploids have been found in Thermopsis, T. gracillis Howell and T. divicarpa A. Nelson (Chen et al., 1994). The chromosome numbers of both Baptisia and Thermopsis are based on x = 9, with 2n = 18 for all species, except for T. gracillis and T. divicarpa, which are 2n = 36 (Chen et al., 1994; Cooper, 1936).
Biochemical evidence suggests that Baptisia evolved from Thermopsis in the southeastern United States (Dement and Mabry, 1975). Two phylogenies of Thermopsidae places T. chinensis and T. villosa in the same clade as several species of Baptisia, including B. australis, based on internal transcribed spacer sequences (Wang et al., 2006; Zhang et al., 2015). Thermopsis interspecific hybrids have not been observed by taxonomists (Dement and Mabry, 1975). However, hybridization readily occurs between species of Baptisia (Alston and Turner, 1963; Baetcke and Alston, 1968; Dement and Mabry, 1975; Larisey, 1940; Leebens-Mack and Milligan, 1998).
In the genus Baptisia, interspecific crosses have been used to create many novel cultivars (Ault, 2003; Avent, 2002; Cullina, 2000), some of which are widely available commercially. Thermopsis has not been used to create hybrids to our knowledge and is also not much known or used in the ornamental plant industry. Many species of Thermopsis, particularly T. villosa, are very tolerant of both drought and heat, making Thermopsis a good substitute for lupines in the southeastern United States (Armitage, 1989). Some species of Thermopsis, such as T. lupinoides, originated in coastal areas and are salt tolerant (Hotes et al., 2001; Probatova and Seledets, 2012). Baptisia has proven difficult to propagate vegetatively through cuttings (Ault, 2003; Cullina, 2000). Thermopsis is easier to root than Baptisia (Hawkins et al., 2013) and will bloom 2 years after germination, whereas Baptisia requires 3 years to bloom from seed (personal communication, Heather Alley, State Botanical Garden of Georgia, 2013).
The overall goal of this project was to investigate the feasibility of hybridization within and between species of Baptisia and Thermopsis. Hybrids could potentially have improved drought tolerance, earlier flowering, and higher rates of rooting compared with the parent species. Ideally, the hybrids would combine desirable ornamental qualities with these improved traits. Hybrids could also serve as bridge parents in future breeding to obtain intergeneric cultivars.
ArmitageA.M.1989Herbaceous perennial plants: A treatise on their identification culture and garden attributes. Varsity Press Athens GA
BaetckeK.P.AlstonR.E.1968The composition of a hybridizing population of Baptisia sphaerocarpa and Baptisia leucophaeaEvolution22157165
CullinaW.2000A guide to growing and propagating native flowers of North America. Houghton Mifflin Co. New York NY
DengY.ChenS.ChangQ.WangH.ChenF.2012The chrysanthemum × Artemisia vulgaris intergeneric hybrid has better rooting ability and higher resistance to alternaria leaf spot than its chrysanthemum parentSci. Hort.134185190
HawkinsS.M.ChappellM.MartinM.T.Jr2013Defining a protocol for vegetative propagation of Baptisia, Eupatorium and ThermopsisJ. Environ. Hort.31162168
HotesS.PoschlodP.SakaiH.InoueT.2001Vegetation, hydrology, and development of a coastal mire in Hokkaido, Japan, affected by flooding and tephra depositionCan. J. Bot.79341361
KatoK.YamaguchiS.ChigiraO.OgawaY.IsodaK.2012Tube pollination using stored pollen for creating Acacia auriculiformis hybridsJ. Trop. For. Sci.24209216
NomuraY.KazumaT.MakaraK.NagaiT.2002Interspecific hybridization of autumn-flowering Allium species with ornamental Alliums and the characteristics of the hybrid plantsSci. Hort.95223237
PolhillR.M.RavenP.H.StirtonC.H.1981Evolution and systematics of the Leguminosae p. 1–26. In: R.M. Polhill and P.H. Raven(eds.). Advances in legume systematics. Royal Botanic Gardens Kew Richmond UK
ProbatovaN.S.SeledetsV.P.2012Ecological ranges and ecological niches of plant species in the monsoon zone of Pacific Russia. 1st ed. Nova Science Publishers Hauppauge NY
TangF.WangH.ChenS.ChenF.LiuZ.FangW.2011Intergeneric hybridization between Dendranthema nankingense and Tanacetum vulgareSci. Hort.13216
WangH.C.YangJ.B.ComptonJ.A.SunH.2006A phylogeny of Thermopsideae (Leguminosae: Papilionoideae) inferred from nuclear ribosomal internal transcribed spacer (ITS) sequencesBot. J. Linn. Soc.151365373
WenJ.NieZ.-L.Ickert-BondS.M.2016Intercontinental disjunctions between eastern Asia and western North America in vascular plants highlight the biogeographic importance of the Bering land bridge from late Cretaceous to NeogeneJ. Syst. Evol.54469490
WuZ.RavenP.H.1994Flora of China. Science Press Beijing; Missouri Botanical Garden St. Louis MO
ZhangM.L.HuangJ.F.SandersonS.C.YanP.WuY.H.PanB.R.2015Molecular biogeography of tribe Thermopsideae (Leguminosae): A Madrean-Tethyan disjunction pattern with an African origin of core GenistoidesBiomed Res. Intl.2015864804