ZHOU Zhong-Ze, ZHAO Zuo-Cheng, WANG Xu-Ying, XU Ren-Xin, LI Yu-Cheng
2003, 41 (1): 63–78
Pollen morphology, and tepal and fruit microcharacteristics of the genus Fagopyrum Mill. (Polygonaceae) from China have been investigated. Pollen grains of ten species and one variety were observed under both light microscope (LM) and scanning electron microscope (SEM). They are prolate, or often subprolate/ prolate to spheroidal in shape, and elliptical from equatorial view, circular from polar view, with their germination aperture being all 3-colporate. Based on the presence or absence of colpus membrane, two types of pollen grains can be recognized in the species studied. In type I, the colpus membrane is visible, and often beset with coarse granules. Four species, F. dibotrys (D.Don) Hara, F esculentum Moench, F. tataricum (L.) Gaertn., and F. statice (Lévl. H. Gross, have this type of pollen grains. In type II, the colpus membrane is invisible. Six species and one variety, F. gracilipes (Hemsl.) Damm. ex Diels, F. leptopodum (Diels) Hedb., F. leptopodum var. grossii (Lévl.) Lauener et Ferguson, F. urophyllum (Bur. et Franch.) H. Gross, F. caudatum (Sam.) A. J. Li, F. gilesii (Hemsl.) Hedb., and F. lineare (Sam.) Harald., have this type of pollen grains. The exine ornamentation in all the species studied is finely reticulate. The exine is very thick. The sexine is thicker than the nexine. The columellae are high, usually branched, and rounded at top in cross-section. The tectum is semi-tectate. To further study the exine ultrastructure, pollen grains of F. esculentum were examined under transmission electron microscope (TEM). The exine is clearly stratified into ectexine and endexine and the ectexine possesses tectum and columellae, but no foot layer. Adaxial tepal surface of the ten species and one variety was observedunder SEM. Three tepal types are recognized based on the shape of epidermal cells and the surface ornamentation. In type I, the epidermal cells are mostly rectangular to narrowly rectangular, with the anticlinal walls being straight or slightly undulating, and the cuticularlayer being longitudinally and undulately striate. This tepal type is found to occur in F. statice and F. urophyllum. In type II, the epidermal cells are elongated and irregular in shape, and strongly ridged, with the anticlinal walls being deeply or shallowly undulating, and the cuticular layer being irregularly anundulately striate. This tepal type is found to occur in F. caudatum, F. lineare, F. gracilipes and F. gilesii. In type III, the epidermal cells are irregular in shape, and are papillose, with the anticlinal walls being straight and prominent, and the cuticular layer being densely and longitudinally striate. This type is found to occur in F. dibotrys, F. esculentum, F. tataricum and F. leptopodum. Fruit surface in the ten species and one variety was observed under SEM. Based on the surface ornamentation, the fruits can be divided into three types. In type I, the fruit surface is striate. This type is found to occur in F. statice, F. caudatum, F. gilesii and F. lineare. In type II, the fruit surface is warty granular, and sparsely striate among the granules. This type is found to occur in F. gracilipes, F. leptopodum, F. leptopodum var. grossii and F. urophyllum In type III, the fruit surface is rugosely striate or striate-reticulate. This type is found to occur in F. dibotrys, F. esculentum and F. tataricum. Evidence from pollen morphology supports the separation of Fagopyrum from Polygonum as an independent genus. Relationships of the Fagopyrum species studied are discussed based on evidence from polen morphology, and from tepal and fruit microcharacteristics. Brief speculation on the evolutionary trends of pollen, tepal and fruit microcharacteristics in the genus Fagopyrum is made.