Identification, sexual dimorphism and aspects of the natural history of Sapria himalayana (Rafflesiaceae) on Vietnam's Lang Biang Plateau

Abstract

Background: Sapria is a distinctive and narrowly host-specific holoparasitic genus belonging to the Rafflesiaceae. Sapria himalayana, rare throughout its range from NE India, SW China, Thailand to Vietnam, is a little-understood species first recorded for Vietnam in 1959, and only recollected there over half a century later in February 2017. This has facilitated an assessment of its taxonomic identity and our understanding of its morphology and natural history aspects.

Results: Six populations of Sapria at Vietnam's Tuyền Lâm Lake, and another two populations at the Nam Ban Protection Forest and the Cam Ly area were found, in an area of about 20 km in radius. Previously documented size attributes, morphological details and colour patterns allowed clear identification of the Vietnamese taxon as Sapria himalayana f. albovinosa. A full description of the species for Vietnam is provided. Past authors have distinguished the sexes by column form and structure, colour of the upper disk, details of the inner surface of the perigone tube, and presence of ovarial chambers below the column in the female. We present additional observations that male flowers consistently have more steeply held perigone lobes than females, in which the lobes were more spread out at wider angles in fully open flowers, and that males have a much lower cupule than females. The latter difference, especially, appears to be useful for quick determination of the sex even in the advanced floral bud stage. The host plant was the lianescent Tetrastigma laoticum (Vitaceae), but superficially it was not possible to ascertain the clonal relationship of neighbouring host lianas. Male and female flowers were found mixed together in the same cluster from one individual liana. Potential pollinators included Calliphorid and Stratiomyid flies observed visiting open flowers.

Conclusions: Our observations have added to an increased understanding of the morphology of this highly specialized parasitic life form. More than this, we have ascertained its occurrence in Vietnam, with information made available to authorities of the Lâm Đồng Province where our studies were conducted, for the sites to be specially demarcated for conservation and carefully managed tourism use.

Keywords: Da Lat; Lang Biang Plateau; Morphology; Parasitic plants; Sapria himalayana; Sexual dimorphism.

Fig. 1

First ever collection of Sapria himalayana Griff. (Tixier s.n.) for Vietnam from the Lang Biang Plateau, as photographed in Tixier (1959), showing female flower in top view (above) and young female flower bud in longitudinal section (below)

Fig. 2

Cross section of the Sapria flower, with morphological parts referred to. A. Basal bracts. B. Perigone lobe. C. Flower diameter. CP. Height of cupule at flower base. D. Circumference of perigone tube at lobe base. E. Perigone lobe width. F. Perigone lobe length. G. Wart. H. Diameter of whole diaphragm. HE. Height of flower. I. Width of diaphragm collar. IB. Basal band. ID. Width of distal band of diaphragm. IM. Width of band of ramenta. J. Width of diaphragm aperture. K. Ramenta. L. Height of perigone tube. M. Ridge on inner surface of perigone tube. N. Flange of ridge on inner surface of perigone tube. O. Fusion area of perigone tube ridges. P. Ovary (in female). Q. Column. S. Height of disk. T. Diameter of crest of disk. U. Depth of disk. WF. Stigmatic fascia (in female). WM. Longitudinal strip of tissue bearing anther (in male). Y. Vestigial anther (in female). Z. Anther (in male) [Based on the original in Bänziger and Hansen (1997), modified by H.Đ. Trần]

Fig. 3

Sapria himalayana Griff. f. albovinosa Bänziger and Hansen, female flower. a Whole flower. b Habitat in natural forest at Tuyen Lam. c Longitudinal section of flower. d Ramenta on upper surface of diaphragm. e Cross section of ovary. f Lateral view of disk and upper part of column, with vestigial anthers (yellow structures in a ring below the disk) visible. g Ovules. Photos: H.Đ. Trần

Fig. 4

Sapria himalayana Griff. f. albovinosa Bänziger and Hansen male flower. a Whole flower. b Open flowers with more steeply held perigone lobes than in the female. c Longitudinal section of flower. d Ramenta on upper surface of diaphragm. e Part of upper disk surface. f Lateral view of column and disk, showing anthers (yellow structures) in a ring and longitudinal ridges on the inner surface of the perigone tube. g Anthers. Photos: H.Đ. Trần

Fig. 5

Sapria himalayana Griff. f. albovinosa Bänziger and Hansen. a Female flower with higher cupule and wider spreading perigone lobes. b Male flower with lower cupule and more steeply held perigone lobes. c Diaphragm and aperture of female flower with a pale disk. d Diaphragm and aperture of male flower, with reddish disk. e Post-anthesis female flower. f Post-anthesis male flower. Photos: H.Đ. Trần

Fig. 6

Tetrastigma laoticum, the host vine of Sapria himalayana. a Mature climbing stem with flat structure due to extended secondary thickening of the original stem axis in opposite directions; demonstrated by Parusuraman Athen. b Leaves with tendrils arising from petiole bases. c Cross section of root near emergence of S. himalayana flower. Photos: H.Đ. Trần

Fig. 7

Sapria himalayana Griff. f. albovinosa Bänziger and Hansen. a Bracts (darker) and perigone lobes (red, patterned) in male flower. b Ramenta in male flower. c Detail of perigone lobe warts and Stratiomyidae fly. d Calliphoridae fly on Sapria flower. Photos: H.Đ. Trần