The Least Specialized Angiosperms

Abstract

To decide which angiospermous groups are the least specialized, one has to form a conception of what features characterized the ancestors of the living angiosperms. For many reasons, this is not an easy task. The relative paucity of the paleobotanical record has resulted in our reconstruction of the evolutionary history of the angiosperms being largely inferential and hypothetical. Fortunately, the flowering plants do supply us with many “living fossils” or nonmissing links, that is, those plants with a plethora of primitive or unspecilized characteristics as recognized by experts such as those listed immediately below. The comprehensive studies by many botanical specialists of these phylogenetic relicts and conservative, that is, archaic, features in their more specialized relatives [Bailey, 1944a, Bailey, 1956, Bailey, 1957; Bailey and Nast, 1943a, Bailey and Nast, 1943b, Bailey and Nast, 1944a, Bailey and Nast, 1944b, Bailey and Nast, 1945, Bailey and Nast, 1948; Bailey et al., 1943; Bailey and Smith, 1942; Bailey and Swamy, 1948, Bailey and Swamy, 1949, Bailey and Swamy, 1951; Canright, 1952, Canright, 1953, Canright, 1955, Canright, 1960, Canright, 1963, Canright, 1965; Carlquist, 1964; Money et al., 1950; Nast, 1944; Nast and Bailey, 1946; Smith, 1947; Swamy, 1949, Swamy, 1952, Swamy, 1953a, Swamy, 1953b, Swamy, 1953c, Swamy, 1953d; Swamy and Bailey, 1950; Wilson, 1960, Wilson, 1964, Wilson, 1965; Wilson and Maculans, 1967; and many others (see references in the works of Thorne, 1974, Thorne, 1976, Thorne, 1981, Thorne, 1983, Thorne, 1992a)] has enabled us to recognize probable ancestral characteristics and the direction of evolutionary trends in many angiosperm organs and tissues, especially in stem and leaf anatomy, pollen grains, ovules, and other embryological structures, floral parts, fruits and seeds, chromosomes, sieve-element plastids, wax crystalloids, and other micromorphological features, biochemical compounds, and so on.