Morphology, Structure, Development And Systematics Of Helleborus Thibetanus Franch. (Ranunculaceae)

Helleborus Linn. (Ranunculaceae) composes of 20 species, and mainly distributed in south Europe and west Asia. Only one specie, H. thibetanus Franch., was found in China, and distributed in west Sichuan, south Gansu, south Shaanxi and northwest Hubei Provinces. The features of anatomy, vessels, floral morphogenesis and embryology of H. thibetanus were described in the present paper. We attempted to supply some new features on the determination of the systematic position of Helleborus in Ranunculaceae. 1. AnatomyThe root tip constitutes of calyptron and apical meristem, and apical meristem is consisted of dermatocalyptrogen, periblem and plerome; The primary structure of root is triarch, tetrarch and hexarch.Xylem of overground organs doesn't show V-shaped appearance. The secondary structure of rhizome include epidem, cortex and vascular tissue, pith ray is developed.The vascular bundles of the primary structure in stem are ring arranged, and the node is unilacunar and 3-traced, which is from three vascular bundles or one vascular bundle.The vascular bundles of the petiole are arranged in arc. Dorsi-ventral leaf, and cells of the leaf pyidermis are irregular and the stomata is anomocytic.On the receptacle, the node of sepals is unilacunar and 3-traced, and the nodes of petals, stamens and carpels are unilacunar and 1-traced. The filament with one vessel bundles; the carpels are connected by the remaining part of the receptacle.There were two types of tracheary elements in the secondary xylem of H. thibetanus, one is the tracheid-like vessel and another is typical vessel elements. Tracheid-like vessels were only observed in stems of H. thibetanus. The typical vessel elements were found in xylem of roots, rhizomes and stems from H. thibetanus universally. Various perforation plates were observed in typical vessels including reticulate perforation plate (including foraminate perforation plate), "Gnetalean type" perforation plate, scalariform perforation plate, reticulate-scalariform perforation plate,...