PHYLOGENETIC Geoffrey A. Levin2 and Michael G. Simpson3IMPLICATIONS OF POLLENULTRASTRUCTURE IN THEOLDFIELDIOIDEAE(EUPHORBIACEAE)'ABSTRACT Th pollen structure of members of Euphorbiaceae subfamilies Oldfieldioideae and Phyllanthoideae was studiedusng scanning and transmission electron microscopy in order to assess taxonomic relationships. We identified 10palynological characters that appear to have systematic significance. We also identified 37 characters of vegetativemorphology and anatomy, mostly based on data obtained by Hayden, and five characters of reproductive morphology,bsed on data in the literature. Cladistic analysis of the Oldfieldioideae along with selected genera m the Phyllanthoideae,uing various putative relatives of the Euphorbiaceae as outgroups, provided great insight into the phylogeny of theOldfieldioideae. Synapomorphies of this subfamily are ail palynological: brevicolporate to pororate or porate apertures,echinate sculpturing, and exine with the interstitium consisting of columellae discontinuous from the foot-layer (wherepresent). With the exception of Croizatia, the basal member of the subfamily, ail Oldfieldioideae also share theynaapomorphies of four or more pollen apertures and no petals; two homoplastic synapomorphies, an exinous foot-lyer that is irregular to absent and a caruncle on the seeds, also characterize these genera. A clade consisting ofParadrypetes and Podocalyx is supported by the synapomorphies of an extremely reduced pollen exine interstitiumand slerified crystalliferous axial xylem parenchyma, whereas the remaining Oldfieldioideae share the synapomorphiesof a "microperforate/baculate" tectum consisting of numerous closely appressed rod-shaped elements, some of whichare continuous with the columellae and/or echinae; uniformly simple perforation plates; and alternate intervascularitting. These Oldfieldioideae represent two clades, taxonomically recognized as the tribes Picrodendreae and Caletieae.The Pirodendreae are diagnosed by the synapomorphy of alternate, circular vessel-ray pitting, and except forTetracoccus, the basal member of the clade, also share four additional synapomorphies, ail foliar: compound orunifoliolate leaves, well-developed bundle sheath extensions, fimbriate marginal ultimate venation, and well-developedareoles. Within the Picrodendreae, synapomorphies distinguish a South American clade and an African/Madagascan/Idian clade, but do not resolve the position of Oldfieldia within the Picrodendreae. The Caletieae share theya orphy of stomatal subsidiary cells that have a crenulate (rather than straight) wall nearest the stomatal pore.Within the tribe, the African genus Hyaenanche is the basal member, with the remaining genera, ail of which areraasin, being united by the synapomorphy of chambered foliar epidermal cells. The Australasian genera comprisetw major clades, but the relationships among these clades and Petalostigma are ambiguous. In addition to clarifyingrltinships within the Oldfieldioideae, these results (1) support the transfer of Croizatia and Paradrypetes fromPhyllanthoideae to the Oldfieldioideae, (2) support inclusion of Scagea, despite its single ovule/locule, in thedeae, (3) demonstrate that Androstachys and Stachyandra are bona fide members of the Oldfieldodeerh thn belonging in their own family, and (4) indicate that Neoroepera, as currently circumscribed, s diphyletic.We propos a revised classification of the subfamily in which all suprageneric taxa are monophyletic accordmg tothis phylogeny. We etend our warmest thanks to John Hayden, who generously shared his data and thoughts with us as wPuhued ou study. Without his generous cooperation, our workwould have been far less complete. We acct futyfor any interpretations that may differ from bis. We thank the curators at DAV, GH, K, MO, P. QIS, SM,. and US for removing or allowing us to remove pollen from collections in their care. Jon Blevitt, Kitty e, and Nicki Watson embedded and sectioned much of the pollen for EM and printed most of the plates sion at the International Conference on the Systematics of the Euphorbiaceae provided valuable insghts. WGrady Webter and Mike Huft for inviting us to partipate. Huft and an anonymos revewermaS com nts on an earlier version of this paper. Levin thank Rick Brca and Regina Wetzer of arinerteebrates Depar t, San Diego Natural History Museum, for allowing him use of their Apple computrs, anSy of the Exhibits Deparment, San Diego Natural History Department, for help with the cladoSe saves hi greatest thanks for Mike Simpson, without whose generous sharing of pollen exp eu tic insight this research would not have been possible. This research was supporte in part by a San Diego ate 'Uty Foundation Grant-in-aid Award to MGS. f ) reof Botany, San Diego Natural History Museumn, P.O. Box 1390, San Diego, California 92112, U.S.A. L rret ad:dr: Center for Biodiversity, Illinois Natural History Survey, 607 East Peabody Drive, Champaig Illuis<>1820, U.S.A. tent of Bology, San Diego State University, San Diego, California 92182, U.S.A. ANN. MISsOURI BOT. GARD. 81: 203-238, 1994.