External Seed Morphology of Arenaria (Caryophyllaceae) of the Southeastern United States

Abstract

Seeds of 13 southeastern United States taxa of Arenaria were exam- ined with the scanning electron microscope. With a few exceptions, external mor- phology is distinctive and valuable for separating taxa at the species level. No dif- ferences were discerned, however, between the closely related A. alabamensis and A. uniflora. Arenaria glabra is variable in the degree of tubercle development, but oth- erwise it is identical to A. groenlandica. Interspecific variation in external seed mor- phology of the taxa examined does not support generic segregation of Minuartia from Arenaria. The scanning electron microscope (SEM) has become the standard tool for the detailed examination of pollen grains, trichomes, seeds, and other morphological features. Brisson and Peterson (1976) reported that SEM seed coat illustrations are available for only 440 species of flowering plants. These data appear to substantiate the contention of Thieret (1966) that ... . characters of vegetative and floral structures have always occupied a position of prominence with systematic botanists, but those of seeds have been little used. Seeds are often ignored in floras and other taxonomic works, although they are generally stable in external morphology (Davis and Heywood 1963). Recently, however, the potential taxonomic value of seed coat microsculpture has been demonstrated by Chuang and Heckard (1972), Hill (1976), Musselman and Mann (1976), Seavey et al. (1977), Newell and Hymowitz (1978), Crow (1979), and Canne (1980). Seed microsculpture has previously been studied in a few taxa of Ar- enaria (sandworts). The seeds of A. ciliata L. subsp. hibernica Ostenf. & Dahl, A. ciliata subsp. pseudofrigida Ostenf. & Dahl (Echlin 1968), and A.