Xyris buengkanensis Phonsena & Chantar., 2012

2. Xyris buengkanensis Phonsena & Chantar. View in CoL , sp. nov. — Fig. 2 View Fig ; Plate 1d, e View Plate 1 , 2c, d View Plate 2 ; Map 1 View Map 1

A congeneribus asiaticis euronotis bracteis pentastichis non imbricatis differt. Bracteae fertiles X. wallichii similissimae in area stomatosa angusta infra-apicali, sed in posteriore angustiore (in priore 2–3-plo longa latiore, versus 3–10-plo in posteriore) et petali limbo fimbriato non integro. — Typus: Phonsena & Sutthisaksopon 6567 (holo KKU; iso BK, BKF, C, L, QBG) , Thailand, Bueng Kan, Si Wilai, Na Sing, Ban Na Sai , alt. 180 m, 8 Oct. 2010. 1 mm

0.1 mm

Etymology. The specific epithet refers to Bueng Kan, the newest province of Thailand, where the type specimens were collected.

Caespitose perennial herb, 20– 50 cm tall. Leave s 5– 35 per plant, ensiform, (8–) 15 –22 cm by 2 – 5 mm, ligulate; blade smooth, margin entire, apex bluntly oblique to acute. Scape terete, 1–1.3 mm thick. Spike ellipsoid, 0.9–1.3 by 0.3 –0.7 cm. Sterile bracts 6–11, in 5 rows, pale brown with hyaline margin, ovate, 4 –7 by 2 – 3 mm, margin entire. Fertile bracts in 5 rows, pale brown with hyaline margin, narrowly elliptic to elliptic, 7–12 by 3–5 mm, margin entire; stomate field triangular, 5–8 by 2 – 3 mm. Lateral sepals hyaline, 7–9 by 1.3 –2 mm with narrow, distantly shortly serrate or entire crest. Petal limbs yellow, obovate to elliptic, 11–14 by 8–10 mm, margin fimbriate. Staminodia bibrachiate, branches elongate-penicillate, 3 – 4 mm long. Anthers oblong, 2–3 mm long, shallowly bifid, deeply sagittate; filaments c. 1 mm long. Style terete, 7–8.5 mm long, distally 3-branched, branches 3– 3.5 mm long. Capsules dark brown, obovoid, 7–8 by 2 – 3 mm. Seeds brown, translucent, ellipsoid, slightly twisted at apex, 0.4 – 0.6 mm long, 0.2 –0.3 mm diam, with 11–14(–15) longitudinal ridges and with 0 –2 transverse ridges between the longitudinal ridges.

Distribution — Endemic to Thailand, North-Eastern: Bueng Kan (Si Wilai), only known from the type locality. It should be looked for in nearby areas within the Mekong basin of Laos and Thailand.

Habitat & Ecology — On open, sandy soil, wet places in dry dipterocarp forest, at 180 m altitude.

Phenology — Flowering: September to November, between the late rainy season and the beginning of the dry season. The flowers open at about 10.30 a.m. and persist until 4.30 p.m.

Vernacular name — Kathin bueng kan.

Specimens examined. Bueng Kan ( Si Wilai, Na Sing, Ban Na Sai , 180 m alt., 18°15'N, 103°46'E): Phonsena 6700 ( BKF, KEP, KKU, L), 31 Dec. 2010 GoogleMaps ; Phonsena & Boonsuk 6423 ( BK, BKF, C, KKU, L), 25 Sept. 2009 ; Phonsena & Boonsuk 6627 ( BKF, KKU, QBG), 28 Nov. 2010 ; Phonsena & Sutthisaksopon 6542 ( BKF, KKU), 8 Aug. 2010 ; Phonsena & Sutthisaksopon 6567 ( BK, BKF, C, K, KKU, L, QBG), 8 Oct. 2010 .

Conservation status — Xyris buengkanensis is endemic to Thailand, and is so far known from only one locality. Its extent of occurrence is estimated as to be less than 100 km 2. Its habitat has been disturbed by farming activities and its occurrence is declining. A rating of Critically Endangered (CR, IUCN 2001) is merited.

Note — The bracts of this species are arranged in five rows but in other SE Asian Xyris they are imbricately arranged. The margin of the bract is hyaline, thin, entire in living plants but mostly fimbriate when dry. The fertile bracts of this species are similar to X. wallichii but the stomate field of the fertile bract in this species is 2 –3 times longer than wide, whereas 3–10 times longer than wide in X. wallichii . Xyris buangkanensis differs also in its fimbriate margin of the petals (entire in X. wallichii ).