A new tribal classification of Mesembryanthemaceae: evidence from floral nectaries

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Abstract:

Mesembryanthemaceae Fenzl, here defined as excluding Aizoaceae Rudolphi s.str., are divided into five major groups, primarily on the basis of characters of the floral nectary. In terms of nectary type, the meronectary is considered a synapomorphy for the family Mesembryanthemaceae. The koilomorphic meronectary is a synapomorphy for subfamily Mesembryanthemoideae, considered the basal group; it is not further divided at tribal level. Four distinct nectary types characterize the more specialized subfamily Ruschioideae Schwantes in Ihlenf., Schwantes & Straka emend. Bittrich & H.E.K. Hartmann, and are used here to establish a new tribal classification for the group. Tribe Apatesieae Schwantes emend. Chesselet, G.F. Sm. & A.E. van Wyk (seven genera) is characterized by a broad, flat holonectary. Fruits in this tribe have diversified and several have lost hygrochastic properties. The group is regarded as primitive among Ruschioideae. Subtribe Dorotheanthinae Schwantes ex Ihlenf. & Struck (three genera) is raised to tribal level as Dorotheantheae (Schwantes ex Ihlenf. & Struck) Chesselet, G.F. Sm. & A.E. van Wyk. Plants in this tribe have semi-succulent leaves and all are annuals. The group has flowers with broad, flat meronectaries, and is not defined by any synapomorphy in terms of nectary type. Tribe Delospermeae Chesselet, G.F. Sm. & A.E. van Wyk (27 genera) is newly proposed to include all taxa with a lophomorphic meronectary; it has diversified mostly in the summer-rainfall region of southern Africa. Tribe Ruschieae, as emended here, incorporates 71 genera. It is characterized by a lophomorphic holonectary and has diversified mostly in the arid winter-rainfall region of southern Africa. Nectary types suggest primitiveness of Delospermeae in relation to Ruschieae among the highly succulent ruschioid taxa and support previous hypotheses suggesting that more derived Ruschioideae originated in the summer-rainfall region of southern Africa.

Keywords: AIZOACEAE; CLASSIFICATION; EVOLUTION; FLOWER; MESEMBRYANTHEMACEAE; NECTARY; NOMENCLATURE; PHYLOGENY; RUSCHIOIDEAE

Document Type: Research Article

Affiliations: 1: Compton Herbarium, National Botanical Institute, Private Bag X7, Claremont 7735, South Africa 2: Office of the Research Director, National Botanical Institute, Private Bag X101, Pretoria 0001, South Africa 3: H. G. W. J. Schweickerdt Herbarium, Department of Botany, University of Pretoria, Pretoria 0002, South Africa

Publication date: May 1, 2002

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