Corethrodendron Fisch. & Basiner

Corethrodendron is a small genus of dryland shrubs from the deserts and steppes of Asia, experiencing cold winters and hot summers in the wild. We include it only by virtue of C. multijugum (still better known to gardeners as Hedysarum multijugum), a small, hardy, sun-loving shrub grown for its long, lax inflorescences of bright rose-purple peaflowers in summer.

Corethrodendron belongs to Tribe Hedysareae of the Fabaceae, a taxonomically troublesome group dominated by the essentially herbaceous genera Hedysarum and Onobrychis (Lewis et al. 2005). As first envisaged in 1845, its sole species was Corethrodendron scoparium (Fisch. & C.A.Mey.) Fisch. & Basiner, an out-and-out desert shrub important for dune fixing across Central Asia and Northern China. Several woody Hedysarum species have recently been transferred to Corethrodendron by Choi & Ohashi (2003). Despite being from the molecular era, this study used only morphological and anatomical features, separating Corethrodendron from Hedysarum by the banner petal not being recurved in the mature flower; by the corolla remaning attached in a withered state to the mature fruit; and by the genuinely shrubby habit, as well as some less easily seen features of the fruit, pollen and stem anatomy. Taken together, molecular studies do not give a clear picture of relationships in the Hedysareae, but support the idea that Corethrodendron is a natural, monophyletic group distinct from Hedysarum (Liu et al. 2017; Amirahmadi et al. 2014), and this wider view of the genus has been widely accepted.

Of the remaining species, one might perhaps be growable in our area, C. krassnowii (B.Fedtsch.) B.H.Choi & H.Ohashi, a mountain plant of rather similar appearance, from the Pamirs. It is distinguished by the 2-lipped rather than campanulate calyx (Xu & Choi 2010).