Leaf architecture of the genus Didymaea Hook. f. (Rubiaceae)

We examined 532 specimens representing eight species of Didymaea (Rubiaceae) to describe their leaf architecture. Characters observed in the herbarium specimens and cleared leaves were leaf base, apex, and margin; trichome type and distribution; vein orders from primary to higher order veins, veinlets, and ultimate marginal vein. Six morphometric variables were analyzed using variance and principal component analysis to identify which characters are useful to distinguish species. Most of the species present brochidodromous venation pattern, except D. hispidula, which has eucamptodromous venation pattern; Didymaeafloribunda is unique in having cylindrical and bicellular trichomes. Principal component analysis revealed that 78% of the total variation is mainly related to leaf maximum width. Variance analysis showed significant differences between D. microflosculosa and the other species. Architectural features were useful for differentiating all the species, and an identification key for the species of Didymaea based only on leaf characters is presented.