Systematic Studies of Eschscholzia (Papaveraceae). II. Seed Coat Microsculpturing

Scanning electron microscope examination of seeds of all thirteen species of Eschscholzia, a genus of western North America, reveals distinguishing features which can be used to separate species, provides evidence of seed flotation as an adaptation to runoff dispersal in some species, and provides additional data toward the resolution of taxonomic and evolutionary problems in the genus. Seed surfaces generally consist of ridges or tubercles of radially elongate cells surrounding facets of tabular cells. Surface features of the mature seed are a function of the collapse of these cells during desiccation. The study of seed coat microsculpturing with the scanning electron microscope has provided taxonomic, evolutionary, and ecological insights in a number of groups. In many cases it has been possible to interpret seed dormancy (Gutterman & Heydecker, 1973), to separate tribes (Whiffin & Tomb, 1972), genera (Mulligan & Bailey, 1976), sections, and even species (Chuang & Heckard, 1972; Ehler, 1976; Hill, 1976; Seavey et al., 1977), and to postulate evolutionary relationships (Chuang & Heckard, 1972; Hill, 1976; Seavey et al., 1977; Whiffin & Tomb, 1972) on the basis of seed coat characteristics. These techniques can be applied profitably to Eschscholzia, a genus of 13 species of western North America. In contrast to seeds of the large genus Papaver, which are exceedingly uniform (Tomb, 1974; but see Gunn & Seldin, 1976), those of Eschscholzia are elaborately sculptured and quite diverse. Seed characters have been used to distinguish species (e.g., E. glyptosperma, E. lobbii) in the past (Greene, 1885, 1905; Jepson, 1922; Munz, 1959). Seeds of E. californica were first examined anatomically by Godfrin (1880), who looked only at mature seeds. Brandza (1891) included this species in his broad study of seed integuments. The first detailed study of the ontogeny of the seed coat was undertaken by Meunier (1891). Shaw (1904) studied the histology of seed coats of E. californica and certain other Papaveraceae. Sachar and Mohan Ram (1958) and Roder (1958) also examined the seed coat of E. californica, the former concurring with previous investigators, the latter differing somewhat, perhaps through inadequacy of observation. Gunn and Seldin (1976) included twelve species (eleven by our reckoning) of Eschscholzia in their light-microscopic study of papaveraceous seeds. They provide a key which separates nine of the species; it includes embryo and color characters, as well as external morphological characBotany, University of California, Davis, CA 95616.