Floral Development And Embryology Of Cardiopteris,Gonocaryum(Cardiopteridaceae) And Gomhandra(Stemonuraceae)

In non-molecular systematic classifications, Cardiopteridaceae was a monotypic family with uncertain systematic position. However, its circumscription has been expanded in molecular era, including at least three genera moved from Icacinaceae s.l. besides Cardiopteris. The expanded Cardiopteridaceae (Cardiopteridaceae s.l.) and Stemonuraceae (a family newly seperated from Icacinaceae s.l.) constitute one of the two subclades of Aquifoliales. Though Cardiopteridaceae s.l. has been greatly supported by molecular data, the family is not easy to recognize morphologically. Cardiopteris is unique in the family, especially its female reproductive structure. In addition, the sister-group relationship of Cardiopteridaceae s.l. and Stemonuraceae also lacks morphological evidence.In this dissertation, floral development and embryology of Cardiopteris, Gonocaryum and Gomphandra were comparatively studied firstly using scanning electron micrography and histological section technique to (1) correctly interpret the unique female reproductive structure of Cardiopteris;(2) clarify the systematic relationship of Cardiopteris and its related groups;(3) seach for respective and common potential morphological synapomorphies of Cardiopteridaceae s.l. and stemonuraceae;(4) infer the possible evolutionary tendency of some characters in Cardiopteridaceae and Stemonuraceae. The major results and conclusions are as follows:1. The gynoecia of Cardiopteris, Gonocaryum and Gomphandra are3-carpellate not2-carpellate or monocarpelate(Gomphandra) as described in documents. Two or three carpels of the gynoecia are reduced at different parts to varied degrees, leading to pseudomonomery. In cardiopteris, one carpel is reduced to a dorsal vascular bundle at the ovary part, but its apex growths into the stigma and style; two carpels are reduced few at the ovary part and constitute the most portion of the ovary wall, but their apices remain as rudiments until anthesis. This different reduction mode leads to functional differentiation among the three carpels. The carpel which has stigma accepts pollen grains and transmits pollen tubes, while the carpels which have no stigma protect the ovules. The fruit appendage of Cardiopteris develops from the intercalary growth of the apices of the two carpels without stigma and the apex of the placental colomn. In Gonocaryum, none of the three carpels are reduced at the ovary part. However, apices of two carpels remain as rudiments above the ovary and only one carpel forms into the stigma and style at the apex. In Gomphandra, two carpels are reduced to one vascular bundle of ovary wall, respectively, and are indistinguishable when the gynoecium is mature. Only one carpel fully develops, forming stigma at the apex and constituting the most portion of the ovary wall.2. The placental vascular bundles of Cardioptes, Gonocaryum and Gomphandra are all connected with the receptacular vascular plexus and with none of the carpellary wall vascular bundles. This indicates that the placentas of the three genera are continuation of the floral apex and are reproductive branches independent from the carpellary wall, not part of the carpels as believed in traditional concept. The apical placentas are presumably derived from the shifting of the central free placenta (with apical ovules) from the center to the periphery and fusion with the ovary wall. The ridges on the inner face of the ovary wall in Gonocaryum and Gomphandra indicate this transition. The ovules are the lateral organs of the placentas. The carpels of the three genera enclose the ovules, but do not produce them. They do not conform to the classic definition of the carpel. However they are the leaf-like structures to protect the ovules.3. Cardiopteris is unique on embryological characters:the ovule is ategmic, the anatropy is delayed, the egg apparatus lies in the chalazal end of the embryo sac, the embryo sac extends from the ovule, and the endosperm haustorium is present. The persistent nucellar tissue encloses the endosperm and the embryo and a vascular bundle differentiates in its median plane. Thus it is similar to seed-coat in structure and function which indicates that the ategmic ovule of Cardiopteris does not lose the integument genes but has no differentiation of the integument and nucellus as the ategmic ovule of Santalales. The delayed curving of the ovule to the seed developmental process maybe results from the delayed expression of genes related to anatropy. The egg apparatus lying at the chalazal end of the embryo sac maybe is related to the delay of the anatropy. Cardiopteris differs from Gonocaryum and Gomphandra and other groups of Aquifoliales in embryological characters. However, it shares several rare characters of Santalales, such as, ategmic ovule, the extra-ovular embryo sac and the well-developed haustorium. It is unsuitable to explain these multiple similarities between Cardiopteris and Santalales merely unsing convergence. The common embryological characters of the two groups probably have the same molecular developmental mechanism.4. The three-carpel late pseudomonomerous gynocium and the cauline placenta fused with the ovary wall are the synapomorphies of Cardiopteridaceae and Stemonuraceae. Cardiopteridaceae s.l. differs from Stemonuraceae in obvious style. The unique embryological characters of Cardiopteris support retaining it as a monotypic family. The highly similarity of the embryological characters between Cardiopteris and Santalales might implie some relationship between their ancestor.