Fruit characters in early divergent Arecaceae-Arecoideae: comparative carpology of Hyophorbe Gaertn. (Chamaedoreeae)

Abstract

ABSTRACT The phylogenetic relationships of two early divergent tribes of Arecoideae (Chamaedoreeae and Iriarteeae) remain poorly resolved. Nevertheless, in some phylogenetic reconstructions the genus Hyophorbe is recognized as the earliest divergent genus of the subfamily. Hence, the fruit anatomy, histogenesis and organogenesis of Hyophorbe species is studied here, with the aim of revealing the key carpological characters of early divergent taxa of Arecaceae – Arecoideae. The multilayered pericarp consists mostly of the mesocarp (parenchymatous cells with different inclusions) and differentiates into outer and inner zones from its early developmental stages (in H. lagenicaulis an additional 1–3 layered inner subdermal zone develops in the inner mesocarp). The one-layered endocarp is represented either by palisade sclereids, lignification of which begins at late developmental stages, or by almost unspecialized thin-walled epidermal cells. The fruits of Hyophorbe species are referred to two different morphogenetic types: the pyrenariums of the Ilex type with a one-layered lignified endocarp (H. lagenicaulis, H. verschaffeltii, H. indica) and berries of the Nuphar type without a continuous lignified zone in the pericarp (H. vaughanii and H. amaricaulis). It is shown that the lignified palisade endocarp could be interpreted as a plesiomorphic character state of Ceroxyloideae – Arecoideae clade, whereas a non-lignified endocarp could be treated as an apomorphy of this clade or a plesiomorphic character state of the family Arecaceae.