A new species of Bauhinia L. (Caesalpinioideae, Leguminosae) from Nakhon Phanom Province, Thailand

Abstract A new liana species of the subfamily Caesalpinioideae (Leguminosae), namely Bauhinia nakhonphanomensis, collected from the Phulangkha National Park, Nakhon Pranom Province, Thailand, is described and illustrated. It is easily recognized by the following combination of characters: tendrilled liana, entire leaves, acuminate or caudate leaf apices, oblong or elliptic floral bud, floral bud 25–35 mm long, raceme or panicle inflorescence, 10–13 mm long hypanthium, anther opening by longitudinal slits. Important comparative morphological characters with some closely related species are discussed.


Introduction
Bauhinia is a large genus belonging to the subfamily Caesalpinioideae (Leguminosae). It is pantropical and consists of approx. 150-160 species (in the strict sense) and is most abundant in the neotropics (Lewis et al. 2005). Th e number of species reaches approx. 300 for the genus when treated in a broader sense Larsen 1984, 1996). Bauhinia comprises trees, shrubs and tendrilled climbers. Its leaves are simple, entire, emarginated, bi-lobed or divided into free leafl ets. Flowers are usually bisexual, with fi ve petals and fi ve sepals; stamens 10, 5, 3, 2 or 1 (Larsen et al. 1984). In Th ailand, Larsen et al. (1984) reported 37 species occurring throughout the country. Th ey also reported that there were six species of tendrilled climbers with entire leaves. During a plant diversity survey carried out in the years 2011-2013 in Phulangka National Park, many specimens of the leaf entire and tendrilled climbers were collected. After careful comparison with known species, it was noted that there was a climber which was quite diff erent from any of the known taxa. Th us, this plant is described here as a new species.
Description. Large tendrilled liana climbing on shrubs or trees or big rocks. Branch glabrous; small young branches straight and the old ones fl attened forming "Monkey-Ladders". Leaves simple; lamina ovate, 7.0-14.5 × 4.0-8.0 cm, palmately netted venation with 5 large veins near the middle and 2 short and small ones marginally; margin entire; apex acuminate or caudate; base rounded to truncate or cordate; both surfaces glabrous excepted for hairs at base of the underside of lamina; young fresh leaves pinkish and green when old. Infl orescences raceme or panicle, terminal or leaf axial; axes greenish and glabrous near base, reddish and covered by densely reddish hairs near apex. Peduncles 35-40 mm long, glabescent. Floral buds oblong or elliptic, 5-ridged, 25-35 × 7-9 mm, apex twisted, reddish-green when fresh and brown when dry. Bracts 1, insert near pedicel base, ovate or lanceolate 8-9 × 4-5 mm, reddish when fresh and brown when dry, sparse minute hairs on abaxial side, dense hairs on adaxial side. Bracteoles 2, insert at the pedicel apex, orbicular or broadly ovate, 10-13 × 9-10 mm, dense reddish-green hairs on adaxial side when fresh and brown when dry, dense hairs on abaxial side when fresh and brown when dry, hairs caducous. Pedicels 28-40 mm long, densely covered with reddish hairs when fresh, the hairs change to be brown when dry. Hypanthium funnel-form , 10-13 mm long, striated. Sepals 5, connate forming an oblong or ellipsoid shape; 5-ridged fl oral buds, splitting into 5 separated and recurved sepals; each sepal linear, 15-20 × 2-3 mm, abaxial side densely hairy, adaxial side sparsely hairy near apex. Petals 5, pinkish, spatulate, acute to obtuse apex; expanded portion 25-32 × 10-12 mm, sparsely covered by whitish hairs on both surfaces; margin entire, densely hairy on upper part and sparsely hairy on lower part; petal claw 15-22 mm long. Stamens 9 -10; fertile stamens 3, fi lament 55-60 mm long, whitish to pinkish, hairy on lower part and glabrous on upper part; anther pink, sparsely hairy and 5-6 mm long and opening by longitudinal slits; sterile stamens 6-7, fi lament 20-24 mm long, anther 2.3-2.5 mm long, hairy and opening by longitudinal slits. Pistil fl attened, reddish, hairy on the two ridges extending from base to the top of style; stipe 15-17 mm; ovary fusiform, 10-12 mm long; styles 12-14 mm long; stigma capitate, approx. 1 mm diameter, glabrous. Fruit not seen.
Flowering and fruiting. fl owering April-July and fruiting unknown. Distribution. Th is new species is an endemic to Th ailand and known from only one location at Phulangka National Park, Ban Pheang District, Nakhon Phanom Province, Th ailand.
Ecology. Th is species grows in a rocky and dense dry evergreen forest at an elevation of 170-240 m. It climbs on small to tall shrubs, trees or on big stones. Some plants grow along the river. Vernacular name. Th ao Khadailing. Etymology. Bauhinia nakhonphanomensis is named after the type locality Nakhon Phanom Province, the northeastern Th ailand.
Discussion. In Th ailand, Bauhinia species can be divided into two groups based upon their habit. Th e fi rst group is comprised of trees or shrubs, while the other is tendrilled climbers. Bauhinia nakhonphanomensis belongs to the latter, but is clearly distinct from the other tendrilled species in having entire leaves with acuminate or caudate leaf apices, oblong or elliptic fl oral buds, fl oral bud 25-35 mm long, raceme or panicle infl orescences, 10-13 mm long hypanthium, and the anther opening by longitudinal slits. When comparing the new species to the other Th ai species, it seems to closely resemble B. concreta Craib, B. curtisii Prain, B. scandens L., B. strychnifolia Craib and B. tubicalyx Craib based on their tendrilled climber habit, entire leaves and anther opening by longitudinal slits. Bauhinia nakhonphanomensis is distinct from these species by having long fl oral buds (i.e. 25-35 mm) and longer pedicels (i.e. 28-40 mm), while B. concreta Craib, B. curtisii Prain, B. scandens L., B. strychnifolia Craib and B. tubicalyx Craib have 12-15 mm fl oral bud lengths and shorter pedicels (2-20 mm) (Larsen et al. 1984).
When comparing this new species to the entire leaf species of Bauhinia in Indo-China, it can be distinguished from the other species based on hypanthium lengths. Th e hypanthium length of Bauhinia nakhonphanomensis is between 10-13 mm, while B. clemensiorum Merrill has 20-25 mm hypanthium length. Of the other entire leaf species, B. calycima Pierre ex Gagnep., B. cardinalis Pierre ex Gagnep, B. championii (Bentham) Bentham, B. curtisii Prainand, and B. scandens L., all have a short to very short hypanthium less than 5 mm long (Larsen et al. 1980).
Bauhinia nakhonphanomensis closely resembles B. exurrens Stapf, known only from Mt Kinabalu Malaysia (Larsen and Larsen 1996). Th e two species are similar to each other by having entire leaves, anthers opening by longitudinal slits, short hypanthium (approx. 10 mm), petals not recurved and long pedicels more than 25 mm. Further diff erences between these two species is shown in Table 1.