The biovulate subfamily Oldfieldioideae of Euphorbiaceae, characterized by spiny pollen, is an otherwise apparently diverse assemblage of mostly Southern Hemisphere trees and shrubs that traditionally have been allied with genera of Phyllanthoideae and Porantheroideae sensu Pax and Hoffmann. Although fairly diverse anatomically, the following structures characterize the subfamily with only a few exceptions: pinnate brochidodromous venation with generally randomly organized tertiary and higher order venation; foliar and petiolar glands absent; unicellular or unbranched uniseriate trichomes; latex absent; mucilaginous epidermis or hypodermis; brachyparacytic stomata; vessel elements with simple perforation plates and alternate, often very small, intervascular pits; thick-walled nonseptate imperforate tracheary elements; numerous narrow heterocellular rays; and abundant axial xylem parenchyma in diffuse to somewhat banded patterns and often bearing prismatic crystals. Anatomically, the shrubby Australian ericoid genera form a well-defined group with obvious affinities to the more arborescent Australasian genera, which show clear relationships to each other; the African and neotropical genera bearing compound leaves form another distinct group; the remaining genera are somewhat more isolated and seem to represent, in various cases, elements that are primitive within the subfamily or elements derived from the group bearing compound leaves. Presence of theoid teeth and palmately compound leaves in Oldfieldioideae are features consistent with Dilleniid origin for Euphorbiaceae.

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Copyright © 1994, Missouri Botanical Garden Press. This article first appeared in Annals of the Missouri Botanical Garden: 81:2 (1994), 180-202.

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