spermatophyte

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spermatophyte

[spər′mad·ə‚fīt]
(botany)
Any one of the seed-bearing vascular plants.
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to evolved at least six times in extant seed plants.
parallel development of diplospermy in other seed plants and other
The female gametophytes of all nonflowering clades of seed plants ultimately function in the nourishment of developing embryos.
In addition, the strategy of exclusively postfertilization development of embryo-nourishing tissues in the female gametophyte is unique among seed plants.
gnemon is compared explicitly to the plesiomorphic developmental patterns expressed in the female gametophytes of basal extant seed plants (cycads and Ginkgo) and to Ephedra, which is basal within Gnetales [ILLUSTRATION FOR FIGURE 1 OMITTED].
Finally, given that most paradigms for the evolution of development have been derived from diverse studies of metazoans, we examine whether basic aspects of developmental evolution in the female gametophytes of seed plants conform to the standard models of heterochrony (Gould 1977; Alberch et al.
This requires clear estimation of the phylogenetic position of Gnetum within the Gnetales and more global hypotheses of the relationships of Gnetales to other groups of seed plants [ILLUSTRATION FOR FIGURE 1 OMITTED].
Finally, it is evident that Ephedra, which is basal among Gnetales, has also retained a pattern of female gametophyte development that is highly similar to that of basal seed plants (Martens 1971; Moussel 1983).
During the cellular phase of development in basal seed plants, female gametophyte cells are initially vacuolate and devoid of any significant nutrient reserves.
1984) and Carboniferous Pachytesta hexangulata (Stewart 1951) demonstrate that the earliest seed plants had female gametopbytes with ontogenies similar to extant cycads and Ginkgo.
Developmental patterns of extant basal seed plant female gametophytes (cycads, Ginkgo) and fossil evidence from some of the earliest known seed plants indicate that the plesiomorphic pattern of somatic female gametophyte ontogeny [TABULAR DATA FOR TABLE 1 OMITTED] among seed plants includes three critical phases: (1) free nuclear development; (2) centripetal cellularization (formation of alveoli); and (3) cellular growth and development accompanied by nutrient provisioning.
The ontogenies of all seed plant female gametophytes are determinate, nonmetameric (the sporophytes of seed plants have an indeterminate and metameric architecture), and as a consequence of being the sexual generation of the life cycle, involve the differentiation of gametes.