MORPHOMETRY OF ORCHID SEEDS. III. NATIVE CALIFORNIA AND RELATED SPECIES OF GOODYERA, PIPERIA, PLATANTHERA AND SPIRANTHES

Morphometric analysis of orchid seeds indicates that testa and embryo dimensions, color and morphology as well as the -presence, absence or nature of reticulation on seed coat walls are of diagnostic value. These studies also point to structure and function correlations in orchid seeds. ORCHID SEEDS are small and consist of an oval embryo enclosed within a generally transparent, often fusiform testa (Arditti, 1967, 1979; Barthlott, 1976; Beer, 1863). Testae and embryos of different genera and species may vary in size, shape, color and the ratios between their volumes (Arditti, Michaud and Healey, in press, a,b). The walls of testa cells can be smooth or reticulated and when reticulation is present its patterns may be distinctive. These morphological properties can serve as taxonomic and/or phylogenetic markers and may also explain certain aspects of orchid seed biology (Barthlott, 1976). For these reasons seed morphometry is one aspect of our research on seeds of native California orchids and related species. MATERIALS AND METHODS-Seeds of Goodyera, Piperia, Platanthera and Spiranthes (Table 1) were prepared and examined as described previously (Arditti, Michaud and Healey, 1979, 1980). Fine structure was studied with a scanning electron microscope (SEM). An optical microscope was used for measurements and color determinations. Seed and embryo dimensions were analyzed statistically (Table 2). OBSERVATIONS-Goodyera testa cells are not reticulated, but their periclinal walls show longitudinal folds (Fig. 1-8). The testae and embryos of all species we examined are brown. Testa cells of G. repens (Fig. 5, 6) are shorter 1 Received for publication 26 June 1979; revision accepted 20 December 1979. Supported by a grant from the Elvinia J. Slosson Fund, received through the Division of Agricultural Sciences, University of California, J. B. Kendrick, Jr., Vice President. We thank the persons listed in Table 1 for seeds and Drs. A. Bennett, T. Gleeson, and R. Putnam for assistance with the statistical analysis. 2 Address for reprint requests. than those of the other three Goodyera species (Table 3). G. pubescens (Fig. 3, 4) has the longest testa cells of the four species studied (Table 3). The seeds of G. repens are more highly truncated (i.e., have a lower length/ width ratio) than the other species (Table 3). Embryos of G. repens are shorter and more spherical (Table 3). Their width does not differ from that of the other species and as a result embryo volume is about average for the genus (Table 3). The seed-volume/embryo-volume ratio as well as percent air space of G. repens are the highest in the genus (Table 3). There are no statistical differences in seed length and width between the North American species G. oblongifolia, G. pubescens and G. tesselata (Table 4). Seeds of the European G. repens are significantly shorter and wider than those of the other three (Table 4). In terms of embryo length, the genus Goodyera separates into three groups, two of them overlapping (Table 5). When embryo width is considered, two overlapping groups are apparent (Table 5). There are significant differences between seed populations of G. oblongifolia, but there are no clear patterns (Table 4). Piperia testa cells have predominantly transverse anastomosing reticulations on their perinclinal walls (Fig. 9-12, 17, 18, 21, 22). Both the testae and embryos are brown (Table 3). The average length of testa cells in all Piperia species is similar. But, due to different seed lengths, the number of cells at the longest axis varies (Table 3). Seed and embryo volumes of P. elegans var elata (Fig. 9, 10) are the smallest in the genus (Table 3). The volume of its embryo is approximately one fifth that of the other embryos. As a consequence, the percent air space inseeds of this species is the highest in the genus (Table 3). In terms of seed length, Piperia species are separated into statistically different populations, three of which are overlapping (Table 6). Seed width of the species