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Evolution of Seed Size, Shape, and Surface Architecture in the Tribe Epilobieae (Onagraceae)

1977; Missouri Botanical Garden; Volume: 64; Issue: 1 Linguagem: Inglês

10.2307/2395235

2162-4372

Steven R. Seavey, Robert E. Magill, Peter H. Raven,

Plant Parasitism and Resistance

he seeds of more than half of the approximately 210 species of Onagraceae tribe Epilobieae were examined with the scanning electron microscope.The six species of Boisduvalia s irregularly angular-fusiform seeds with convex, flat, irregularly polygonal surface cells 1 two species and an irregularly striated reticulum formed by the unevenly joining walls of the surface cells in the four others.They are similar to one another and RUE distinct from those of Epilobium, although the relationship between the genera is undoubtedly close.The seeds of Epilobium fall in seven groups: (1) large, obovoid seeds with a more or less prominent micropylar constriction, in three small sections of generalized peel rad ben in one species, E. rigidum, of sect.Epilobium; (2) smaller papillose seeds in over hal the other species;(3) 5 seeds, indepe tidenfiy evolved in many species; (4) 1 patelliform seeds in four Australasian species; (5) irregularly reticulate seeds in one subsection of Epilobium sect.5 6) ric ged seeds in a ä coherent group of North American origin; (7) finely papillose, distinctive seeds in sect.ssostigma.More or less prominent chalazal beaks have evolved in some species.From xe 1 ic ancestors, Epilobium has evolved a highly successful group of e in sect.Epilobium that have achieved worldwide distribution.This trend seems to have been accompanied by an increase in seed number and a concomitant decrease in very size.The well-marked tribe Epilobieae, one of six that make up the family Onagraceae, includes some 200 species of Epilobium, of worldwide distribution; and six of Boisduvalia, five of western North America, with one common to Argentina, and one additional species restricted to western South America.The western North American Zauschneria, often recognized as distinct from Epilobium, is based on a red-flowered, bird-pollinated species of one of the constituent groups of Epilobium.Zauschneria has accordingly been reduced to the status of a section of Epilobium (Raven, 1976).Of the six sections of Epilobium, two, with a total of three species, consist of annuals and are restricted to western North America; two others, with a total of four species, are generalized xerophytic perennials of western North America; one, Chamaenerion, includes seven species of Eurasia, two of which extend to North America; and the remaining one, sect.Epilobium, consists of some 185 species, found on every continent except Antarctica, but especially well represented at high altitudes and high latitudes.The surface sculpturing of the seeds of Epilobium has long been employed as an important taxonomic character (cf.Haussknecht, 1884;Samuelsson, 1923, The authors are grateful to the U.S.