A new species from Thailand and Burma, Dracaena kaweesakii Wilkin & Suksathan (Asparagaceae subfamily Nolinoideae)

Abstract A morphologically distinct element of the group of Dracaena species from Thailand and Burma with undifferentiated leaf sheaths, no leaf blade central costa, free tepals and free thickened filaments known as Chan nuu or Chan pha krai in Thai is shown to be a distinct species, Dracaena kaweesakii Wilkin & Suksathan based on habit, leaf base and margin, inflorescence axis indumentum and floral characters. It is described and illustrated. Ecological and conservation status assessment information are provided.


Introduction
Th e taxonomy of the "dragon tree" group of Dracaena L. species in mainland South-East Asia was summarised in Wilkin et al. (2012). Th e species possess an undiff erentiated leaf sheath, lack a leaf blade central costa and have free tepals and free thickened fi laments. Th ree species with this set of characters are recognised in the World Checklist of Monocotyledons (WCM, Govaerts et al. 2011), Dracaena cambodiana Pierre ex Gagnep., Dracaena cochinchinensis (Lour.) S.C.Chen and Dracaena yuccifolia Ridl. Th e WCM suggests that there are a total of 15 species of Dracaena in Th ailand. A further "dragon tree" species occurs in South-East Asian and Pacifi c islands, D. multifl ora Warb. ex Sarasin (Wong et al. 1999).
In addition to the three accepted names in Govaerts et al. (2011) and D. jayniana Wilkin & Suksathan that was described in Wilkin et al. (2012), a further element of the "dragon tree" group of species usually known as Chan nuu or Chan pa krai in Th ai appeared distinct in its macromorphology from all other related taxa. Th us it was investigated more closely to discover if it represented an undescribed taxon.

Materials and methods
Th is research involved comparative morphological study of living plants of the "dragon tree" group of Dracaena in the fi eld and in cultivation in Th ailand and of the specimens cited below. Further specimens of Dracaena from the herbaria BM, BK, BKF, QGB, C, K, L, P and WAG were examined. In order to test the hypothesis that Chan nuu/Chan pa krai represented a distinct taxon it was compared directly with D. yuccifolia (Ridley 1896) and with D. cambodiana , D. cochinchinensis , D. jayniana and D. multifl ora . Th e principal characters used are listed in Table 1.

Results
Both Dracaena yuccifolia and Chan nuu / Chan pa krai diff er from other taxa of the Asian "dragon tree" group of Dracaena species in their much-branched habit (there may be several hundred branches in large mature trees of Chan nuu ), with spreading and dividing branches usually borne on a short, unbranched basal trunk. Th ey also possess narrow terminal branches, usually less than 2 cm in diameter near the leafy apices. Th e other taxa, D. cochinchinensis , D. cambodiana , D. jayniana and D. multifl ora (Gagnepain 1934, Wong et al. 1999, Chen and Turland 2000 usually have not more than 10 erect or ascending stems bearing few erect to decumbent branches which are not spreading. Th eir terminal branches are more robust, being at least 2.4 cm in diameter. Th e latter taxa also possess thicker leaf blades with stronger longitudinal costae than D. yuccifolia and the entity under study, in which the leaf blades are relatively thin and soft. Table 1 shows the main morphological diff erences between D. yuccifolia and Chan nuu/Chan pa krai . It is clear that the habit, vegetative and reproductive morphology of the latter are distinct from that of the former species. Th us it is described as a new species below. Diagnosis. Dracaena kaweesakii diff ers from Dracaena yuccifolia Ridl. in its habit, with up to several hundred branches, white (brown when dry) leaf sheaths lacking yellow or dark brown pigmentation and blades with a narrow white margin when fresh. Th e infl orescence axis of D. kaweesakii is tuberculate-villous, and the species lacks a fl oral stalk above the pedicel articulation. Th e tepals are cream-green or cream-yellow and Description. Underground organs unknown. Indumentum absent except for infl orescence axes and pedicels with tuberculate-villous trichomes to 0.15 mm long, often dense, sometimes crisped; similar trichomes on margins of leaves and tepal bases and margins. Habit treelike, 3-6 m(-12) m in height at maturity with an approximately equivalent crown diameter; usually much-branched, branches spreading and dividing, with up to several hundred terminal branches in large mature trees, branches rarely as few as ca 10 (mainly in high altitude forms such as those on Doi Chiang Dao). Trunk base to 1 m in diameter, sometimes markedly thicker than where branching begins, usually at ca 30-100 cm above the soil surface, epidermis brown, grey or ashwhite, corky and fi ssured except at branch apices, enclosing cream-coloured, densely fi brous parenchyma, less dense towards centre, denser and heavier than that of D. jayniana . Leaf scars present in apical 30-50 cm of branches where diam. is 1.3-2.4 cm (to 4.2 cm some cultivated plants e.g. Wilkin et al. 1521 perhaps due to increased nutrient availability), epidermis grey to light brown with tightly packed scars. Leaves in dense clusters of ca 20-50 leaves at shoot apices, clusters ca 30-120 cm in diam., 7-10 youngest leaves ascending to spreading, older recurved-pendent; divided into a basal sheath and blade, not pseudopetiolate; sheaths 8-16 × 17-32 mm, ovate to ovate-triangular, white (pale brown to mid brown when dry) sometimes with some irregular red markings from dried sap, sheath base clasping stem apex for ca 180°; leaf blades 11-60.5 × 0.9-3.1 cm, lorate-acuminate to linear-acuminate, not or weakly thickened above sheath, softer in texture than other Th ai Dracaena species occurring on limestone, dark to mid green, thickly chartaceous to thinly coriaceous with a weak longitudinal central costa that is barely visible in apical half of the blade, primary venation parallel, dense sometimes denser in costa than elsewhere, secondary venation not visible; margins ca 1 mm broad and white when fresh, 0.1-0.3 mm wide when dry, to 0.5 mm on sheath, translucent white or pale brown, entire to bearing scattered trichomes, sometimes quite dense on sheath, often concealed by rolling of margins during drying; apex acuminate, terminated by a ca 1.5 mm long blunt, angular apiculus, translucent white to pale brown when dry, similar in appearance to margins. Infl orescence terminal on shoot, apical, erect or ascending relative to shoot growth direction in fl ower but can become pendent in fruit due to their mass, with 4 levels of branching; peduncle (0.8-)3.2-15.5 cm long, primary fertile axis ca 25-38 cm long; partial infl orescences racemose, with a primary axis and fl owers in glomerular clusters or solitary towards axis apex; peduncular bracts to 8.7 cm long, foliaceous but with a reduced sheath, lower primary axis bracts to 7.5 cm long, foliaceous, becoming smaller towards apex, ovate-acuminate to broadly so and increasingly brown and scarious towards axis apex, morphologically continuous with bracts of secondary and tertiary axes and glomerular bracts, secondary branches 3.4-19.1 cm long, tertiary branches 1.9-6.2 cm long; glomerules (fourth level of infl orescence branching) composed of 1-3 fl owers, internodes between glomerules to 10 mm in length, glomerular bracts 1.2-1.6 × 0.6-1.5 mm, ovate to broadly so, acuminate to acute, pale brown, scarious, clasping glomerule base, fl oral bracts like glomerular bracts but smaller and tending to be acute rather than acuminate, clasping pedicel base. Flowers patent to axis to ascending on a 1.2-2.0 × 0.3-0.7 mm, terete-angular pedicel, expanded and articulated at its apex; fl oral stalk absent, with 0.5-0.8 × 1.0-1.4 mm receptacle inserted directly on pedicel apex; tepals 6.0-8.5 × 1.2-2.6 mm long, narrowly oblong to oblong-elliptic or oblonglanceolate, free almost to base, erect, with apical half recurved, cream with a green or yellow hue, paler and more translucent towards margins, greener towards apex and along thickened longitudinal costa, apex cucullate, acute to rounded, margins towards apex bearing a fringe of translucent trichomes; fi laments 2.2-3.8 × 0.4-0.7 mm (free part), erect, narrowly lanceoloid, thickened, intense orange, green at base and where fused to tepal base, orange colour derived from bundles of heavily pigmented cells in translucent matrix; anthers dorsifi xed, before anthesis 1.7-2.2 × 0.4-0.7(-1.0) mm, pale yellow, oblongoid; ovary 2.4-3.3 × 1.3-2.0 mm, ellipsoid to narrowly obovoid, pale green, 3-locular, with an apical swelling at the apex of each vertical loculicidal dehiscence line, swelling minutely verrucate and surrounding point of style insertion, style 2.5-3.3 mm long, erect, terete, white, stigma 0.5-0.8 mm in diam, 3-lobed, capitate. Infructescence usually with most bracts fallen, trichomes substantially persistent. Fruit a berry, tepal remains persistent at base, each berry bearing 1-3 seeds, 6.6-8.3 × 7-8.5 mm and (sub)globose (where 1-seeded), 7.0-8.2 × 9.9-11.3 mm (2-seeded) or 8.3-8.8 × 11.2-12.0 mm (3-seeded) and lobed, light to mid brown, becoming orange at maturity but most orange fruit already fallen, when dry with a paler cap around point of style base insertion sometimes bearing stylar remains. Seeds ca 6-7 mm in diam., globose to broadly triquetrous, pale brown, smooth but microreticulate.

Dracaena kaweesakii
Distribution . Specimens seen from northern, northeastern and central Th ailand, but ancedotal evidence exists as to extensive distribution in adjacent Burma (Fig. 4) through oral reports of the Burmese workers at Doi Ang Khang, which is on the Th ailand/Burma border.  In higher mountains on ridge tops ( Chan pa krai form) and on the slopes and/or summits where they occur on lower limestone mountains in Loei and Lop Buri Provinces of Th ailand. Higher altitude forms tend to be smaller, with fewer branches, a more open crown and smaller leaves, especially when in more exposed habitats. However, trees to ca 8 m in height and diam. and 50 cm DBH can be found in dense montane forest on limestone ridges at high altitude in northern Th ailand.
Conservation status. As indicated in Fig. 4, there are two groups of lowland populations of Dracaena kaweesakii , in Saraburi and Lop Buri (Central Th ailand), where we have reports supported by photographs of seven populations in addition to the localities represented by Wilkin et al. 1500 and Sriponamat 2 and 3. It is found near Nong Hin in Loei Province (northeastern Th ailand). Th ere are three known localities in northern Th ailand; at Doi Chiang Dao and near Doi Ang Khang and Mae Sai. Th ese population locations were imported into GeoCAT (Bachman et al. 2011;http://geocat.kew.org/) and extent of occurrence (EOO) was calculated to be 73, 657 km 2 , while area of occupancy (AOO) was calculated to be 44 km 2 based on a cell width of 2 km. However, anecdotal reports suggest the species is also distributed well into Burma on limestone ridges. Th e authors have seen populations of 10s to 100s of individuals and we have received reports of seven populations with sizes from eight to 150 mature plants in Saraburi and Lop Buri Provinces, suggesting that there are likely to be a few hundred plants in central Th ailand. Th ere appear to be few plants of Chan pa krai on Doi Chiang Dao. Th us it is likely that even including its distribution in Burma there would be less than 2, 500 mature individuals, the threshold for criterion C of EN (IUCN 2001).
Dracaena kaweesakii is extracted from the wild for use in horticulture in Th ailand and is one of the more popular taxa due to its extensive branching. A number of populations are protected by proximity to temples or having been transplanted into their gardens. Th ere is no evidence yet of over-extraction but sustainability studies are needed at population level; the authors have, for example, encountered an alley of vegetation being cleared to remove D. kaweesakii from a limestone karst in Loei Province. Limestone habitats are generally threatened in Th ailand by extraction for concrete manufacture, especially those closest to cities such as Bangkok; the populations in Saraburi and Lop Buri are the most vulnerable to this threat. Fires can also be problematic. Th us a preliminary assessment of Endangered (EN B2b (ii, iii, iv, v) C1) based on the criteria of IUCN (2001) is indicated.
Uses. Used in horticult ure in Th ailand. Etymology. Th is species is named for our collaborator, friend and co-author Toi (Keeratkiat Kaweesak) to recognise of his extensive knowledge of Chan diversity.
Notes. As indicated in Table 1, Dracaena kaweesakii diff ers from Dracaena yuccifolia in both vegetative and reproductive characters. It has up to several hundred branches, while the latter does not exceed about 80. Th e leaf sheaths are white (brown when dry) and lack the yellow or dark brown pigmentation found in D. kaweesakii . Th e leaf blades of D. kaweesakii possess a distinctive a narrow white margin when fresh. Th e infl orescence axis of D. kaweesakii is tuberculate-villous not glabrous to microaculeate, and it lacks a fl oral stalk above the pedicel articulation; thus the fl ower is inserted directly at the pedicel apex. Th e tepals of D. kaweesakii are cream-green or cream-yellow, with intense orange fi laments (as opposed to bright white tepals and fi laments), the anthers 1.7-2.2 mm long (as opposed to1.0-1.4 mm) and the style 2.2-3.3 mm long (as opposed to 3.4-5.5 mm). Th e ovary is broader (1.3-2.0 versus 0.5-1.1 mm) and fruits that largely remain brown on the infructescence, turning orange only just before or after falling (dull light red on the infructescence in D. yuccifolia ).
Two specimens collected on Hainan Island, How 70949 & Lau 225 may belong to an expanded concept of this species or a morphologically distinct close relative. Both have relatively thin leaves with pale margins and narrow terminal shoots; fl oral colour and dimensions also appear similar to those of D. kaweesakii (e.g. tepals ca 6.5 mm long), although there are no fl owers at anthesis on those specimens. Th ey both diff er in possessing glabrous infl orescence axes, up to 5 fl owers per glomerule and a stalk above the point of articulation of the pedicel. Neither is D. cochinchinensis as they have been determined. Both specimens possess a few leaves and an infl orescence with a few closed fl owers. Th e taxonomy of Dracaena with free tepals in Hainan needs urgent revision including fi eldbased study of fertile plants, not least to provide conservation status information.
Th e fruits of D. kaweesakii were said to be dispersed by squirrels at Nong Hin in Loei Province. Th is may explain the late transition from brown to orange in colour around the time of fruit fall. Other species in Th ailand have dull red fruits on the infructescence, bird dispersal appears likely. Field studies are needed to test these hypotheses.