|其他摘要||The phylogenetic relationships of Quercus subg. Cyclobalanopsis were comprehensively investigated using integrated studies on comparative embryology, fruit anatomy, palynology, leaf anatomy and molecular phylogeny, along with field and herbarium investigations. The taxonomy of Quercus subg. Cyclobalanopsis was revised. The results are summarized as follows:
1. Comparative embryology, fruit anatomy and cladistic analysis
Embryologic features of Quercus subg. Cyclobalanopsis are reported for the first time. The anther wall is five to six layered with a basic type of development (including a persistent epidermis, a fibrous endothecium, two to three ephemeral middle layers and a secretory anther tapetum). Simultaneous cytokinesis during microsporogenesis follows meiosis of the microspore mother cell, thereby forming a tetrahedral. The mature pollen grain is two or three-celled.
Ovules are bitegmic-crassinucellate and anatropous. The inner and outer integuments together form a micropyle. The sporogeneous cell (sometimes several cells) of the nucellus functions directly as a megaspore mother cell (cells), later developing into one to three tetrads. The tetrad is arranged in a line or a “T” shape, within which only one random megaspore develops into a functional megaspore, which later develops into a polygonum-type embryo sac with ephemeral antipodal cells. Two polar cells occur beneath the egg apparatus and fuse before fertilization. The development of endosperm is of the Nuclear Type and the embryo sac possesses hypostase.
Other embryological and fruit characters (ovary cavities, trichomes in locule, size of ovules relative to the ovary cavity, and if aborted ovules are attached to the elongate septum) indicate that subg. Cyclobalanopsis has a closer relation to sect. Cerris, than other taxa in Quercus s.s. Elongation of the placenta, the potential synapomorphy of the two taxa, represents the primitive status in Fagacaeae. Increasing the volume of the style (especially the parenchyma in the style) in pistillate flowers demonstrates a better adaptive strategy to the long term delayed fertilization in the Fagales. These results support the basal position of the subg. Cyclobalanopsis and sect. Cerris in Quercus s.l..
Cladistic analysis based on 25 embryological and fruit characters supported the monophyletic status of Quercus s.l. Subg. Cyclobalanopsis - the basal group and having a closer relationship to sect. Cerris than other sections in subg. Quercus. This was supported by tree topology, but without a bootstrap value. Additional characters related to the comparative anatomy of the cotyledon region, and the pericarp, should be investigated to help understand the phylogeny of Quercus s.l. Trigonobalanus, a basal group within the Fagaceae is systematically closer to Castanea than to Quercus.
The apertures in pollen grains of Quercus subg. Cyclobalanopsis have little taxonomic significance and can be classified into 3 types: uniform rod or spinulate tufts (type I), fine granulate (type II), and verrucate and rugulae (type III).
The pollen sculptures of subg. Cyclobalanopsis are similar to those of the section Cerris, but are different from those species having the tuberculate or complex verrucate sculptures of sections Quercus, Lobatae and Protobalanus. All pollen characters support the intragenus status of the Cyclobalanopsis. Two morphological evolutionary trends are discussed. Type I pollen is the primitive type within Quercus s.l.. The other pollen extine is derived either by fusion of the rods, spinulate, or by thickening on special sites on the extine of type I pollen.
3. Cladistic analysis of morphologic characters
Two groups can be discriminated within the subg. Cyclobalanopsis: a complex trichome basal cells group (CTB) and a simple trichome basal cell group (STB). On the lower cuticle, CTB presents smooth wax ornamentation, obviously irregular interspaces between secondary veins and frequently presenting intersecondary veins, which is similar to sect. Cerris. The STB group has a cruciate wax scale, regularly spaced secondary veins, and rarely presents intersecondary veins. Simple stellate trichomes and complex trichomes are distinct structures with different lineages and are not related.. The complex trichome basal cells were only found in sections Helferiana, Gilva, Lepidotricha and Cerris. In sect. Gilva and sect. Lepidotricha, the thick-walled uniseriate and bulbous glandular trichomes were also observed for the first time within subg. Cyclobalanopsis. Two-armed no-glandular trichomes and pappilae structures are the synapomorphies to the species in sect Glauca and sect. Semiserrata respectively.
Cladistic analysis on 51 cuticle, stomata, venation and acorn characters also demonstrated the two lineages: CTB and STB. Within STB, a pappilae group and a lateral-appressed trichome-uniseries group can be discriminated from tree topology. Additional reweighting of the characters stages and adding more characters on anthers and stigmas are necessary to achieve sufficient bootstrap value.
4. Molecular phylogeny
A phylogenetic analysis of 51 species of subg. Cyclobalanopsis, based on nuclear ITS sequences, was used to investigate phylogenetic relationships within the subg. Cyclobalanopsis. The monophyletic status of Quercus s.l. was confirmed and data supported the subgenus status of Cyclobalanopsis. Two clades exist in Quercus s.l.: sect. Quercus+sect. Protobalanus vs. Sect. Cerris+subg. Cyclobalanopsis. Within the latter clade, a complex trichome basal cells lineage and a simple trichome basal cell lineage were detected. The Sect. Cerris is nested within the complex trichome basal cells group indicating the basal position of the complex trichome basal cell group within subg. Cyclobalanopsis. Plastid psbA-trnH did not help to solve the phylogenetic relationships within subg. Cyclobalanopsis, due to its uniform sequences. More data sequences from single or low copies of nuclear DNA are needed to improve the phylogenetic solution.
5. Taxonomic revision
The systematic taxonomy of Quercus subg. Cyclobalanopsis was revised based on these results and field observations. Quercus subg. Cyclobalanopsis was divided into six sections: Helferiana,. Gilva, Glauca, Pachyloma,. Oidocarpa, and Chrysotrichae.
Section Helferiana and section Gilva are the basal groups within the subgenus with obvious complexed trichome basal cells and primitive venation characters. These two sections have a close relation to sect. Cerris subsect. Lepidobalanus. The Section. Cyclobalanopsis possesses an obvious elongate inflorescence, and has distinct differences from other simple trichome basal cell groups. Section Pachyloma is characterized by large global or oblong acorns, glabrous leaves with pappilaes. Section Glauca, having two-armed no- glandular trichomes and typical uniseriate glandular trichomes, is the most advanced section in subg. Cyclobalanopsis. Section Chrysotrichae shares some characters of sect. Pachyloma and sect. Glauca, indicating that it links the two sections.
Eighty-nine species and 9 varieties of Quercus subg. Cyclobalanopsis are recognized worldwide. In China, fifty-eight species and 9 varieties are recognized. Among them, seven species were enumerated as dubious taxa because of the unavailability of type specimens or ambiguous original publication citations. Twenty species were reduced to synonymies. Eight new combinations are proposed. The confused taxonomy in the Q. glauca and Q. oxyodon complexes was clarified.|