Phyllostylon

Abstract: In two associated families, Celtidaceae and Ulmaceae, vernation pattern (represented by spatial relationships between leaf lamina and stipules, the presence or absence of stipular fusion, lamina orientation, and lamina folding pattern) is consistent within a genus but shows a significant diversity within a family. Six vernation types are distinguishable and tentatively named: 1) Celtis type (Aphananthe, Celtis, Lozanella, Parasponia, Pteroceltis, Trema), 2) Chaetachme type (Chaetachme), 3) Gironniera type (Gironniera), 4) Holoptelea type (Ampelocera, Holoptelea, Phyllostylon), 5) Zelkova type (Hemiptelea, Planera, Zelkova), and 6) Ulmus type (Ulmus). The former three types (found in most of celtidaceous genera) possess free or fused stipules inside of the lamina; in contrast, the latter three types (found in all six ulmaceous genera andAmpelocera) are characterized by having the free stipules outside of the lamina. Within Celtidaceae, Celtis type is probably primitive in having free stipules and an ordinarily oriented lamina; Chaetachme type (with fused, convolute stipules and obliquely oriented laminas) and Gironniera type (with laterally oriented laminas) are the derived. Likewise, within Ulmaceae, both Zelkova and Ulmus types (with laterally oriented laminas) are the derived, while Holoptelea type (with ordinarily oriented laminas) is primitive. Comparisons in vernation pattern suggest the distinctness of Celtidaceae from Ulmaceae and the isolated position ofAmpelocera.