Seed cone structure in conifers in relation to development and pollination: a biological approach

Abstract

Seed production in conifers involves an extended sequence of developmental events that may take as long as 3 years to complete. There is a conflict between two major processes: initial pollination of ovules and subsequent maturation of seeds after fertilization. The conflict arises because ovules must be exposed at first to receive pollen (the gymno-ovulate condition), and subsequently seeds must be protected during maturation (the angiospermous condition). The "Florin model", which shows that the coniferous cone was ancestrally a compound structure, provides a constructional "Bauplan" whose modifications can be understood by developmental study. In the majority of conifers there is no consistent ovule-bearing structure, even though this is required by the model; much of cone ontogeny is determined by intercalary meristematic activity that results in cone closure after pollination. Two main constructional types can be recognized. In Cephalotaxaceae, Cupressaceae, Sciadopityaceae, Taxaceae, and Taxodiaceae (all without saccate pollen), pollen structure and function is uniform and not associated with special modification of the ovulate cone at the time of pollen capture. In the Pinaceae and Podocarpaceae (mostly with saccate pollen), the ovulate cone is usually highly specialized with regard to pollen capture. In the former group, developmental emphasis is on postpollination events that lead to seed protection or are associated with seed dispersal. In the latter group, there is a duality in ovulate cone morphology, initially associated with pollination, and subsequently with seed protection and dispersal. The general conclusion is that the coniferous cone cannot be treated as a static entity for comparative purposes. The functional attributes of cone structures need to be considered in a very broad context when the evolution of the coniferous cone is discussed.Key words: conifers, development, pollen capture, seed cone.

Conifer ovulate cones accumulate pollen principally by simple impaction

“…But then what is its adaptive function? We do not consider the broad requirements for protecting the ovules and maturing and dispersing the seeds, which are reviewed elsewhere (20). Instead, we offer two further adaptive interpretations.…”

Phylogenetic Analysis of Araucariaceae: Integrating Molecules, Morphology, and Fossils

“…Ovulate cones in most Podocarpaceae consist of one or more fertile units, each composed of a fertile bract subtending an axillary epimatium that bears a single adaxial inverted ovule. In our matrix, the podocarpaceous epimatium was postulated as homologous to the bract/scale complex tissues enclosing the seed in Araucaria (table B1) because it represents the most accepted theory (Tomlinson and Takaso 2002). However, the reconstruction of this character on the MPT is ambiguous for Araucariaceae, and therefore, it is not possible to support one state as derived or primitive for this character.…”

A Biased, Misleading Review on Early Angiosperms

“…Although angio-ovuly is the only consistent difference that separates angiosperms from gymnosperms [11,18,36], Herendeen et al [1] added three more features to the criterion and, incredibly, they failed to Natural Science obey their OWN rule themselves because the first "exemplar" early angiosperm Monetianthus does satisfy their own criterion! Herendeen et al [1] rejected Juraherba bodae as an angiosperm based on an excuse: "the leaf is too thin" (a feature not among the criterion they proposed).…”

“…These pre-Cretaceous angiosperms were recognized on the basis of presence of enclosed ovules, a feature proposed and applied by various authors [11,18,36]. Such a parsimony in wording has little to with authority of Herendeen et al but reflects their diffidence in their treatments.…”