Cavea tanguensis

The erect unbranching stems are stout and 5–25 cm high. The leaves in the basal rosette are somewhat leathery or even fleshy, the underside with many or few brownish glandular hairs, elongated spoon-shaped, 1+1⁄2–6 or exceptionally 12 cm long and 1⁄2–1 cm wide, at the base gradually narrowing to the main vein, the edge with some teeth far apart, and a blunt tip or almost pointy. The leaves on the stem have brownish glandular hairs, with some saw-like teeth and a blunt tip. The lower leaves on the stem are 3–6 cm long and 1⁄2–1¼ cm wide. Leaves become smaller and less leathery or fleshy further up, with the highest bract-like, up to 1+1⁄2 cm, almost vertically oriented and enveloping the base of the flower heads.[2]

Flower heads mostly contain relatively few male florets at the centre, encircled by many more female florets. However solely female flower heads also occur, and individual plants may even produce only female flower heads. The flower heads are individually set at the end of the branches, bowl-shaped and mostly 3–3+1⁄2 cm across. The involucre is 1+1⁄2–2 cm high, nearly reaching the mouth of the florets, with four to five whorls of leaf-like bracts, the outermost bracts largest, which are long to very long ovate in shape linear-oblong or obovate-lanceolate, their margin with some glandular hairs, and a stump to pointy tip. The common base of the floret is flat or somewhat convex, and is without bracts subtending individual florets. Each flower head contains a hundred to two hundred very slender disk florets. There are usually, twenty to thirty male florets at the centre of a flower head, which are tube- to bell-shaped, with five lobes, the tube being about 4+1⁄2 mm long, and the free part of the lobes about 4 mm long. In the male florets, the stigma does not split into lobes. The sterile cypselae are about 11 mm long, hairless except for one whorl of pappus hairs of about 5 mm at the tip. The female florets are purplish in color, tube-shaped, densely covered in hard white hairs, with a tube of about 7 mm long and lobes of less than ¼ mm. In the female florets, the stigmas have two lobes, the lobes being exserted inside the corolla tube. The cypselae in the female florets are slender, angular cylindrical, 5–6 mm, set with dense bristles and two whorls of about fifty rough, purple pappus hairs of about 7+1⁄2 mm. Flowers are present in July and August, while ripe fruits can be found in September and October.[2]

The pollen grains are about 35 μm in diameter, slightly flattened at the poles, with three longitudinal slits that suddenly stop near the poles. The surface is densely covered in conical spines of 2–4+1⁄2 μm high and 1+3⁄4–2+1⁄2 μm wide at the base, slightly perforated at base, and with pointy tips.[3]

Gymnarrhena micrantha is now considered the sister taxon of Cavea tanguensis, who together constitute the tribe Gymnarrheneae and the subfamily Gymnarrhenoideae.[4][5]

Based on recent genetic analysis, it is now generally accepted that the Pertyoideae subfamily is sister to a clade that has as its basal member the Gymnarrhenoideae, and further consists of the Asteroideae, Corymbioideae and Cichorioideae. These three subfamilies share a deletion of nine base-pairs in the ndhF gene which is not present in Gymnarrhena micrantha. Current insights in the relationships of Cavea and Gymnarrhena to the closest Asterid subfamilies is represented by the following tree.[4][5]

Cavea is named after George Cave, who was the curator of the Lloyd's Botanical Garden in Darjeeling, and who collected many new plants from all over Sikkim.[6]