Studies on the Ecological and Physiological Significance of Amphicarpy in Gymnarrhena micrantha (Compositae)

Abstract

The 2 types of fruit (aerial and subterranean) borne by the dwarf desert annual Gymnarrhena micrantha were compared with regard to their responses to factors affecting their formation, dispersal, germination and seedling mortality. The 2 types of fruit differed markedly in several respects. In comparison with the subterranean fruits, the aerial ones are much smaller and more numerous, but the formation of the inflorescence in which they develop is more dependent on a favorable supply of soil moisture. The aerial fruits are dispersed by wind, after becoming detached by a complex series of hygroscopic movements which involve several organs and tissues, while the subterranean fruits never leave the dead parent plant, germinating right through its tissues. Germination of the subterranean fruits starts after a shorter incubation period and is less temperature‐dependent in both light and dark. Light stimulated germination of both types of fruit, increasing their germination rates and final percentages, but not affecting the duration of the incubation period. In the subterranean fruits, the rate of germination was equally stimulated by light over the entire temperature range, with a well‐defined optimum at 15 C in both light and dark. In the aerial fruits, the same optimum was found only in the light, rates in darkness increasing with decreasing temperatures. In the aerial fruits, alternations of light and dark were more favorable to germination than either continuous light or dark, the full effect being obtained with a single 8‐hr or 16‐hr light period, provided it was preceded by 16 or 8 hr of darkness, respectively. Similar reactions to combinations of light and dark were not observed in the subterranean fruits. Seedlings developing from the subterranean fruits were much larger, but grew at a relatively much slower rate than those from aerial fruits. The former were distinctly more tolerant of unfavorable soil‐moisture regimes, such as low moisture supply and drought. It was concluded that the 2 types of fruit serve 2 distinct functions in the biology of the plant. The aerial fruits are adapted to the function of increasing the distribution of the species within suitable habitats, while the subterranean fruits are adapted to increasing the probability of the survival of the species.

Not only size matters: achene morphology affects time of seedling emergence in three heterocarpic species of <i>Anacyclus</i> (Anthemideae, Asteraceae)

“…Heterocarpic species in this family usually produce different achene morphs within the same capitulum (reviewed in Imbert, 2002), although exceptions in which achene variation occurs between aerial and subterranean capitula are known in Gymnarrhena micrantha (Koller & Roth, 1964) and Catananche lutea (Ruiz de Clavijo, 1995;Ruiz de Clavijo & Jiménez, 1998), and in Centaurea melitensis (Porras & Muñoz, 2000) between cleistogamous and chasmogamous capitula. Apart from these exceptions, most of achene variation is found within capitula.…”

How does seed heteromorphism influence the life history stages of Atriplex sagittata (Chenopodiaceae)?

“…In the genus Atriplex, it is confined to annual species of salt marshes, semideserts and deserts, and there is a strong tendency for functional divergence of particular seed types, each being specialized on some aspect of temporally and spatially heterogeneous environment (Manda´k and Pysˇek, 1998, 1999a, 2001a, see also Donohue, 1997;Koller and Roth, 1964;Venable and Levin, 1985a, b).…”

“…Fruit size in seed heteromorphic plants is usually associated with differences in shape, colour or presence of various appendages (Manda´k, 1997) and with marked differences in ecological properties. These differences may reflect within-or between-year timing of germination (Baker and O'Dowd, 1982;De Clavijo, 1994Manda´k and Pysˇek, 2001a;McEvoy, 1984;Kigel, 1992;Tanowitz et al, 1987;Yamaguchi et al, 1990), dispersal (Koller and Roth, 1964;Manda´k and Pysˇek, 2001b;McEvoy and Cox, 1987;Rocha, 1996;Sorenson, 1978), seed bank dynamics (Manda´k and Pysˇek, 2001b;Wertis and Ungar, 1986), dormancy patterns (Bra¨ndel, 2004), competitive abilities (Flint and Palmblad, 1978;Imbert et al, 1997;Venable, 1985a), survival and fecundity schedules (Cheplick and Quinn, 1982), or vulnerability to predation (Cook et al, 1971).…”

Achene dimorphism in Bidens pilosa L. (Asteraceae) as determined by germination test

“…This meant that the short achenes (5 mm long) of the first harvest was of the same size that the long achenes (5 mm long) while short achenes were 3 mm long in the last harvest. The presence of polymorphic achenes has been reported by KOLLER and ROTH (1964) …”