During a recent plant collecting expedition (May 2002) sponsored by the U.S. National Geographic Society to the northern part of Ha Giang Prov. (Quan Ba Distr., Thai An Municipality, in the vicinity of Lo Thang village, latitude 23059’50”N, longitude 105005’46”E), we collected a specimen of Lysimachia (HAL 1502) that represents a species unknown in the flora of Vietnam.The plant was growing in crevices of hight vertical eroded solid crystalline white marble-like limestone cliffs under light shade of primary closed evergreen submontane coniferous forest (co-dominants are Pseudotsuga sinensis, Tsuga chinensis and Pinus kwangtungensis), sometimes mixed with broad-leaved species (such as Quercus spp. and Lithocarpus spp.) at elevation of about 1400 m a.s.l. The most distinguishing character from all Lysimachia species known hitherto in Indochina in general, in Vietnam in particular, is its linear leaf blades. It was later identified as L. vittiformis F.H. Chen & C.M. Hu, a new record for the flora of Vietnam.
L. vittiformis is a parennial herb or small undershrub, subwoody at base, glabrous, erect, to 0.3-0.5 m tall. Stems are usually numerous, copiously minutely glandular at apex. Leaves are spirally arranged; petioles short, 2-3 mm long; leaf blades linear, (25-) 40-70 (-90) x (1.8-) 2-2.5 (-3) mm, papery, often slightly falcate, margin narrowly revolute; midveins raised more abaxially than cluster ed 2-3; pedicels filiform, 1.5-2.5 cm long, elongating to 3cm in fruit. Calyx lobes are elongate triangular,ca. 1.5 x 0.5 mm, glandular on margins and inside, apex acuminate. Corollas are 5-6 mm, deeply parted; lobes shortly linear or lanceolate, ca. 4-5 x 1.5-2.5 (-3) mm, overlapping to right, apex obtuse. Filaments are connate basally into a ca. 0.4 mm high ring, fused with corolla, free part ca. 0.5 mm; anthers elongate sagittate, mucronate at apex, ca. 3.3 x 0.6 mm, basifixed, opening by apical pores. Styles are ca. 4 mm long, slender. Capsules are globose, ca. 3 x 1.5 mm.
This species bloms in April-June, fruits ripen in May-July. It grows in submontane belt where the climate is a monsoon tropical one associated with mountains where the mean annual temperature is about 16.50C with at least 7 cold months with the monthly mean temperature is below 170C and the mean annual total of precipitation is over 2500 mm with no dry months.
This species is known before only from the type locaity, presumed to be endemic to Guangxi. With our findings, it is considered now as a narrow endemic to the South Chinese-North-East Vietnam floristic province. This demonstrates once again that in the Northeastern region of Vietnam there are not a few species that are found also in the southeasternmost part of China, not a few of them are endemic to above-cited floristic province. On the other hand the North-East of Vietnam, especially its limestone mountainous areas, comprise one of the regions with the highest level of plant diversity and the richest level of endemism.
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