Miliusa microphylla Damth. & Chaowasku, 2022

Damthongdee, Anissara, Sinbumroong, Aroon, Rueangruea, Sukid, Kaitongsuk, Saksan, Ue-Aree, Phasit, Jongsook, Hathaichanok & Chaowasku, Tanawat, 2022, Miliusa microphylla (Annonaceae), a new species from Thailand as evidenced by morphology and plastid phylogeny, with M. glandulifera, a new record for Thailand, Phytotaxa 532 (3), pp. 259-274 : 263-267

Miliusa microphylla Damth. & Chaowasku , sp. nov. ( Figs. 2A , 3A–F , 4 , 5 )

Type:— THAILAND. Chanthaburi: Khao Soi Dao Wildlife Sanctuary, Khao Soi Dao Waterfall, 13°1’60’’ N, 102°10’0’’ E, 21 Oct. 2001, Koonkhunthod 154 (holotype: BKF! [ SN 216231; Fig. 4 ], isotypes: BKF!), in flower .

Diagnosis:— Miliusa microphylla is closely related to M. mollis , but differs in having longer flowering pedicels; glandular structures that are distinct (brownish black in living plants; vs. less distinct and ± light brown in living plants), ± crescent-shaped (vs. ± semicircular) and located about 1 mm above the base (vs. located at the base) inside the inner petals; and short intermixed with long dense hairs on margin (and area near margin on the adaxial side) of the inner petals (best observable on the apical half; vs. only short dense hairs on margin [and apical area near margin on the adaxial side] of the inner petals).

Description:— Treelets or shrubs to 8 m tall; young twigs villous with erect hairs, intermixed with shorter hairs. Petiole absent to 0.5 mm long, villous with erect hairs (when petiole present); leaf blade (narrowly) ovate to (narrowly) ovateelliptic, sometimes ± subcircular (mostly first leaves of twigs), 2.7–5.3 × 1–2 cm, lower surface tomentose-villous with erect hairs, upper surface glabrous, base subcordate, unequal, sometimes slightly clasping twigs on one side, apex acute to acute-acuminate, seldom obtuse or rounded; midrib slightly raised and villous with erect hairs on lower surface, hairs becoming sparser towards apex, slightly sunken and tomentose with erect hairs on upper surface, becoming flatter with sparser hairs towards apex; secondary veins 8–10 per side, rather indistinct, angle with midrib 45°–65° (at middle part of leaf blade). Inflorescences 1- or 2-flowered, axillary or in axils of fallen leaves; flowers greenish cream in vivo, buds ± depressed triangular pyramid; peduncle inconspicuous when present, almost glabrous, bracts observed, broadly ovate to triangular; pedicel 12–15 mm long, almost glabrous, bearing 1 ovate-triangular bract near base. Sepals connate at base, broadly ovate-triangular, persistent in fruit, 0.8–1 × 1–1.3 mm, outside almost glabrous to pilose with erect hairs, inside glabrous, margin puberulous-tomentose with erect hairs. Outer petals (broadly) ovate, 1.5 × 1–1.3 mm, outside almost glabrous, inside glabrous, margin tomentose with erect hairs; inner petals broadly ovate, 3 × 3.3–3.5 mm, glabrous on both sides, margin (and near margin on inner side) villous with erect and appressed hairs, intermixed with shorter hairs (best observable on apical half), apex of inner petals broadly acute, ± crescentshaped glandular structures present inside, ca. 1 mm higher than base. Torus depressed hemispherical. Stamens 11–13 per flower, 0.8–1 mm long, connective prolongation nearly absent. Carpels 5–7 per flower, 0.8–1 mm long; stigmas subglobose; ovaries glabrous; ovule 1 per ovary, basal. Fruit consisting of up to 4 monocarps, black in vivo, borne on a pedicel to 22 mm long, seed-bearing portion of monocarps subglobose, ca. 7 × 6 mm, smooth, glabrous, not apiculate, stipe 3–3.5 mm long, glabrous. Seed 1 per monocarp, subglobose, ca. 6.5 × 5.5 mm.

Etymology:— The epithet refers to the considerably small leaves of this species, which is one of the species with smallest leaves in Annonaceae .

Habitat:— Occurs in (partially disturbed) evergreen forests, sometimes on a limestone mountain; at an elevation of 100– 400 m.

Phenology:— Flowering material collected in May, September–November; fruiting material collected in May– September.

Distribution:— Endemic to southeastern Thailand ( Fig. 5 ).

Conservation status:— EN B2ab(iii) according to IUCN Standards and Petitions Committee (2019). This species is known by two locations ( Fig. 5 ), one of which is Khao Soi Dao Wildlife Sanctuary (right location in Fig. 5 ), another is Bo Tong District of Chonburi Province (left location in Fig. 5 ). The latter is not in protected areas and, therefore, highly likely to be disturbed by human activities. In the Khao Soi Dao Wildlife Sanctuary, a number of individuals were found (personal observations, TC) and it is anticipated that M. microphylla occurs throughout the sanctuary at low elevation (100–400 m). Consequently, the estimated AOO (area of occupancy) is higher than 10 km 2 but lower than 500 km 2.

Vernacular name:— Jing Jaab Kiw Khem (Thai).

Additional specimens studied (paratypes):— THAILAND. Chanthaburi: Khao Soi Dao Wildlife Sanctuary , 12°45’ N, 102°10’ E, 13 May 1974, Geesink et al. 6746 ( BKF, L) ; Khao Soi Dao Wildlife Sanctuary , 13°6’ N, 102°10’ E, 13 Feb. 2002, Kessler PK 3207 ( L) ; Khao Soi Dao Wildlife Sanctuary , 13°1’60’’ N, 102°10’ E, 20 Sep. 1999, Koonkhunthod 49 ( BKF) ; Khao Soi Dao Wildlife Sanctuary , 13°1’60’’ N, 102°10’ E, 7 Nov. 1999, Koonkhunthod 59 ( BKF) ; Khao Soi Dao Wildlife Sanctuary , 12°56’ N, 102°13’ E, 9 Sep. 1999, Middleton 183 ( BKF) ; Khao Soi Dao Wildlife Sanctuary , 8 Nov. 1998, Pholsena 1756 ( L) ; Khao Soi Dao Wildlife Sanctuary , 13°5’33.1’’ N, 102°10’21.2’’ E, 24 May 2013, Tagane et al. T1477 ( BKF) ; Chonburi: Bo Tong, Khao Kam Pang , 14 Jul. 1999, Puudjaa & Cholkulchana 598 ( BKF) ; Cultivated (originally from Khao Soi Dao Wildlife Sanctuary ), unknown date, Chaowasku 49 and 172 ( CMUB) .

It is noteworthy that M. microphylla was phytochemically studied in Sawasdee et al. (2010, 2013; as M. mollis ). Miliusa mollis has the widest distribution among the species in clade C. It occurs in several Thai provinces, including Surat Thani of peninsular Thailand (= Miliusa mollis 3 in Fig. 1 , new record for the region), as well as in Cambodia (type) and Vietnam ( Fig. 5 ). It is worthwhile to note that the statement that this species is absent in Vietnam ( Chaowasku & Kessler 2014) is incorrect; the gathering Harmand 3274 (P) collected in Chaudoc was not seen by Chaowasku & Kessler (2014).

Although M. glandulifera is the sister group of a clade embracing M. microphylla and M. mollis , no synapomorphic features uniting the three species have been observed. Similarly, synapomorphies of a clade composed of M. amplexicaulis and M. nakhonsiana have not been found yet. The leaf base of the two species is considerably different ( Mols & Kessler 2003; Chaowasku & Kessler 2013), with that of M. nakhonsiana being much more asymmetrical and clasping, resembling that of M. sessilis (Chaowasku & Kessler 2013) . Therefore, the high degree of leaf-base asymmetry and clasping of M. nakhonsiana and M. sessilis is likely to involve independent developments. Regarding the sister relationship of M. intermedia and M. sessilis , so far observed they only share nearly sessile to very shortly stipitate monocarps (stipe up to 1.5 mm long), but the monocarps of M. glandulifera are also quite short-stiped (stipe 1.5–2.5 mm long), whereas the stipe is ≥ 3 mm long in M. amplexicaulis , M. microphylla , M. mollis and M. nakhonsiana ( Mols & Kessler 2003; Chaowasku & Kessler 2013).

With the availability of fruiting material, the description of M. glandulifera is emended as follows:

Figures

FIGURE 1. Phylogram derived from Bayesian inference, with support values indicated: PP (posterior probabilities) / BS (maximum likelihood bootstrap values) / SR (parsimony symmetric resampling values). ** = BS and/or SR <50%. Scale bar unit: substitutions per site.

FIGURE 2. A. Flower of member in clade CM2 (= Miliusa microphylla, sp. nov.), apical view. B. Flower of member in clade CM1 (= Miliusa mollis), apical view. C. Flower of Miliusa glandulifera, apical view. D. Mature monocarps of Miliusa glandulifera. Photographs by A. Damthongdee (C, D) and T. Chaowasku (A, B).

FIGURE 3. A–F. Floral organs of member in clade CM2 (= Miliusa microphylla, sp. nov.). A. Adaxial side of inner petal. B. Abaxial side of inner petal. C. Back view of flower, showing sepals and outer petals. D. Flower with stamens and carpels enlarged. E. Carpel. F.Adaxial (above) and abaxial (below) sides of stamen. G. Adaxial side of inner petal of member in clade CM1 (= Miliusa mollis). From Chaowasku 172 (CMUB; A–F) and Smitinand 7455 (BKF; G).

FIGURE 4. Holotype of Miliusa microphylla, sp. nov. (Koonkhunthod 154 [SN216231], BKF).

FIGURE 5. Distribution of Miliusa glandulifera (squares), Miliusa microphylla, sp. nov. (triangles) and Miliusa mollis (circles).