Embryology of the Irvingiaceae,a family with uncertain relationships among the Malpighiales |
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Authors: | Hiroshi Tobe Peter H Raven |
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Institution: | (1) Department of Botany, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan;(2) Missouri Botanical Garden, P.O. Box 299, St. Louis, MO 63166, USA |
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Abstract: | The Irvingiaceae, one of 40 families of the Malpighiales, comprise a small woody family of 10 species in three genera distributed
in Old World tropics. Its relationships with other families are unclear, although recent molecular analyses suggest affinities
with Linaceae, Caryocaraceae, Erythroxylaceae, and Rhizophoraceae. To gain insight into family relationships, we investigated
63 embryological characters of two previously unstudied African species, Irvingia gabonensis and I. smithii, and compared them with other Malpighiales and the sister group Oxalidales. Embryologically, Irvingia is characterized by the absence of an integumentary tapetum and by having a non-multiplicative inner integument, a multiplicative
testa, many discrete fascicles of vascular bundles running in the testa from the raphe to antiraphe (each fascicle comprised
several strands arranged in a concentric manner), and a fibrous exotegmen. Comparisons showed that Irvingia did not resemble any of the Linaceae, Caryocaraceae, Erythroxylaceae, Rhizophoraceae, or any of the other malpighialean families
for which embryological data are available. The genus rather resembled Huaceae and Connaraceae (Oxalidales) in seed coat structure.
However, 18 families (45%) of the Malpighiales are still poorly understood embryologically, and therefore additional studies
are required for further critical comparisons. |
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