Morphological observation of vessel elements in secondary xylem of Ribes

The Ribes is a genus with higher economic value while the morphology of this genus varies significantly. Flowers can be unisexual or bisexual as two complex groups; therefore, the classification of its subgenera is considerably difficult. In order to provide valuable reference for the phylogeny of this genus, the morphological structure of vessel elements of 20 species of seven subgenera of Ribes were observed and compared by using light microscope and scanning electron microscope. The main results are as follows. 1) The vessel elements of Ribes are pitted and threaded, and have tails with varied length in all the seven subgenera. 2) The vessel elements of Ribes are thin and small, with the length ranging from 250 to 440 μm and the diameter from 15 to 30 μm. 3) Perforated plate type is mainly scalariform and the average number of bars is 5.2 to 11.0, the angle of side walls is smaller, ranging from 13.33 to 18.95 degree, and does not vary much among species, with R. mandshuricum, R. triste, R. moupinense var. muliense and R. luridum presenting reticulate-scalariform transitional perforated plate and R. alpestre, R. vilmorinii and R. fasciculatum var. chinense bearing scalariform-simple transitional perforated plate. 4) There are lateral-wall perforation plates in R. odoratum, R. girdldii var. polyanthum and R. moupinense var. muliense. 5) There are solely alternate pitting pattern, or both alternate pitting and opposite pitting pattern, while the pit shape shows some variations such as round, near round, rhombus, strip and linear type. 6) The shapes of the inner wall of the vessel elements vary. Most of them are smooth and some are rough ones that have round protrusions of different sizes or reticular projections comprised of round protrusions of varying sizes.