TAXONOMIC SIGNIFICANCE OF PERICARP AND SEED STRUCTURE IN HEERIA-ARGENTEA (THUNB) MEISN (ANACARDIACEAE), INCLUDING REFERENCE PACHYCHALAZY AND RECALCITRANCE

Heeria argentea (tribe Rhoeae), a monotypic, dioecious tree, is endemi c to the core area of the Cape Floristic Region. The mature exocarp co nsists of a uniseriate layer of palisade-like epidermal cells, intersp ersed with modified stomata. The mature endocarp sensu stricto develop s solely from the inner epidermis. It is essentially two-layered and r esembles the state in Protorhus longifolia. This endocarp is here prop osed as a distinct fourth endocarpal subtype under the so-called Anaca rdium-type. The large, pachychalazal, recalcitrant seed develops from the single, anatropous, bitegmic, crassinucellate ovule. This ovule is characterized by an extensive chalaza, vascularization and Anacardiac eae-type hypostase. The pachychalazal seed coat contains abundant vasc ular bundles and a tanniniferous hypostase. The inner epidermis of the inner integument differentiates into an endotegmen. The contribution of the integuments towards seed coat development is negligible. Concer ning characters of the disc in the female newer, the meso- and endocar p, as well as seed size, degree of pachychalazy, nutrient reserves (st arch) in the chlorophyllous cotyledons and hypogeal germination, Heeri a shows a very close phylogenetic relationship to Protorhus longifolia . However, fruit and seed structure clearly supports the taxonomic sep aration of Heeria from Ozoroa. Data also support the view that Heeria is a tropical relict, and the hypothesis that pachychalazy, greater se ed size, as well as recalcitrant seed viability behaviour constitute a ncestral seed character states. Pachychalazy is regarded as a function al adaptation for more efficient transfer of nutrients. (C) 1996 The L innean Society of London