干旱区生态环境知识资源中心

Protorhus namaquensis Sprague (Anacardiaceae, Rhoeae) is a rare, small tree of restricted distribution in an extremely arid part of southern Africa. The ovule is bitegmic, anatropous, and crassinucellar. Its hypostase extends secondarily together with the chalaza, forming a prominent part of the mature chalazal seed coat. An endotegmen, which develops from the inner epidermis of the inner integument, characterizes the integumentary seed coat and merges into the periphery of the chalazal seed coat in the partially pachychalazal seed. A comparison of the ovule and exalbuminous seed of P. namaquensis with those of P. longifalia (the lectotype of the genus Protorhus) and species of Ozoroa provides ample evidence that P. namaquensis is associated with members of the genus Ozoroa, rather than with P. longifolia. It is suggested that the very late impregnation with callose of the hypostase cell walls in P. namaquensis evolved as a response to its harsh semi-desert habitat. This callose deposition, together with the cuticular layer on the inner surface of the endotegmen, cutins in the hypostase cell walls, and deposits of tannin in the seed coat, probably constitute micromorphological survival strategies of this