Ardisia crenata Sims subsp. mukdahanensis Chatan & Promprom, 2024

Promprom, Wilawan, Munglue, Phukphon & Chatan, Wannachai, 2024, Ardisia crenata subsp. mukdahanensis, a new subspecies of Primulaceae from Thailand, PhytoKeys 247, pp. 1-10 : 1-10

Ardisia crenata Sims subsp. mukdahanensis Chatan & Promprom sp. nov.

Figs 1 , 2 , 3 , 4

Type.

Thailand • Dong Luang District , Mukdahan Province, alt. 220–250 m, 16 ° 46 ' 23 " N, 104 ° 21 ' 58 " E, 10 November 2023 (fl.), W. Chatan 2886 (holotype: BKF!; isotype: BK!) .

Diagnosis.

Ardisia crenata subsp. mukdahanensis is closely related to subsp. crassinervosa . However, the morphological distinctions of the new subspecies from the latter are as follows: moderately dense, minute hairs are present on the surfaces of young shoots, the abaxial side of the lamina (with very few or sparse hairs on older ones), peduncles, pedicels and the abaxial side of the calyx of the new subspecies, while they are absent in the latter. It has larger flowers (7.0– 7.5 mm) that are typically pure white or pinkish. The fruits are mostly larger (7–8 mm in diameter) and glandular punctation is absent in the lamina, calyx, corolla, anther and fruit in the new subspecies, whereas they are present in the latter.

Description.

Shrubs 40–100 cm high; branchlets slender, terete or angular, striate, generally each branch bearing more than 10 leaves. Leaves alternate, petioles 0.4–2.0 cm long; lamina subcoriaceous, oblanceolate or oblanceolate-oblong, 5–20 × 1.5–4 cm; base cuneate or attenuate; margin distinctly crenate and recurved, with large marginal glands on sinuses; adaxial surface glabrous or glabrescent, glandular dots absent; apices mostly obtuse, rarely acute; abaxial surface with very few minute hairs and sparsely hairs on the mid-rib, glandular dots absent; veins distinct; intramarginal veins present at 1.5–2.5 mm from the lamina edge at the middle between the marginal glands and those veins close to the margin by joining to the marginal glands. Inflorescences sub-umbellate or corymbiform, mostly simple or occasionally compound, terminal on branchlets; peduncles 0.4–0.5 cm long moderately dense minute hairs on the surface; bract oblong and V-shaped, 8–11 × 2.0– 2.5 mm, primary rachis 2–6 mm long; pedicels 8–10 mm long, cylindrical, green, surface with moderate hairs. Calyx of 5 - lobes, split almost to the base, pale green on both surfaces, distinctly imbricate at base; lobes broadly ovate, 3.0–3.5 × 2.5–3.0 mm, glandular-dots absent, apices acute or obtuse, margin entire and translucent, adaxially glabrous, abaxially covered with moderately dense minute hairs. Corolla of 5 - lobes, connate at about 1 mm at the base, pure white or pinkish, sometimes pinkish only at base and centre, thick and succulent, lobes convolute in bud, broadly ovate, concavo-convex, 7.0–7.5 × 4.5–5 mm, glandular-dots absent on both surfaces, apex mucronate with curved mucro. Stamen 5; filament whitish, ca. 1 mm long; anther lanceolate, yellow, 5.0–5.5 × 1.8–2.1 mm, apex acute, glandular dots absent. Gynoecium length is longer than the stamen; ovary globose, 1.4–1.6 mm diameter, green, glabrous, 7 locules, 1 ovule in each locule, ovules in 1 - series; styles about 4.5–5.0 mm long, irregularly curved and narrow to the apex, sparsely minute hairs on the lower half; stigma minute. Fruits young green, mature red, globose, 7–8 mm diameter, glandular dots absent. Seed globular, 4.0– 4.5 mm diameter, brown.

Additional specimen examined.

Thailand • Dong Luang District, Mukdahan Province: Phu Pha Yol National Park , alt. 220–250 m, 16 ° 46 ' 42.3 " N, 104 ° 21 ' 25.6 " E, 1 September 2021 (fr.), W. Chatan 2504 (paratype: BKF) .

Distribution.

Ardisia crenata subsp. mukdahanensis is an endemic to Thailand. So far, it has been only found in the type locality in Dong Luang District, Mukdahan Province. Its distribution is shown in Fig. 5 .

Ecology.

It mostly grows in slightly dense dry evergreen forests or open areas and usually grows near the stream. Sometimes it grows in dry-dipterocarp forests.

Phenology.

Flowering in May to November and fruiting in June to February.

Vernacular name.

Takai Kao.

Etymology.

The specific epithet ‘ mukdahanensis ’ refers to its type locality, the Mukdahan Province, in the northeast of Thailand.

Provisional conservation status.

Currently, A. crenata subsp. mukdahanensis is known only from its type locality. Comprehensive fieldwork is needed to conduct a thorough conservation assessment. Therefore, the species is classified as Data Deficient ( DD) according to the Guidelines for using the IUCN Red List Categories and Criteria ( IUCN Standards and Petitions Committee 2024).

Palynology.

The pollen grains of A. crenata subsp. mukdahanensis are monads, semi-angular in polar shape, oblate-spheroidal in equatorial shape, small size, 11.50 ± 1.30 µm in equatorial axis, 10.20 ± 1.20 µm in polar, radially symmetrical, isopolar, tricolpate, separate apertures at the pollen pole, exine sculpturing foveolate-reticulate, perforate (Fig. 6 ).

Notes.

In the most recent update of classification, A. crenata was classified into three subspecies: A. crenata subsp. crenata , A. crenata subsp. crassinervosa and A. crenata subsp. obtusifolia ( Chatan and Promprom 2017 b) . The discovery of A. crenata subsp. mukdahanensis has expanded this to four subspecies within A. crenata . Ardisia crenata subsp. mukdahanensis is most closely related to A. crenata subsp. crassinervosa , but it differs by having the following distinct characteristics: moderately dense, minute hairs present on the surfaces of young shoots, the abaxial side of the lamina (with very few or sparse hairs on older ones), peduncles, pedicels and the abaxial side of the calyx, whereas these hairs are absent in the latter. Additionally, A. crenata subsp. mukdahanensis typically has larger flowers (7.0– 7.5 mm vs. 4–5 mm) that are pure white or pinkish (vs. pink or purplish), larger fruits (7–8 mm vs. ca. 5 mm in diameter) and lack glandular punctation in the lamina, calyx, corolla, anther and fruit, which are present in A. crenata subsp. crassinervosa (Figs 1 – 4 ). Details of the morphological differences are shown in Table 1 .

Several key characteristics can distinguish the new subspecies from the other subspecies. Compared to A. crenata subsp. crenata , the new subspecies has a subcoriaceous lamina (vs. chartaceous or subcoriaceous), a mostly obtuse lamina apex (vs. mostly acute or acuminate) and broadly ovate calyx-lobes (vs. ovate or ovate-oblong). In contrast to A. crenata subsp. obtusifolia , the new subspecies differs in having a subcoriaceous lamina (vs. highly coriaceous), an oblanceolate or oblanceolate-oblong leaf shape (vs. spathulate, narrowly elliptic or oblanceolate) and distinctly crenate and recurved on leaf margin (vs. sub-entire or shallowly crenate, undulate). In summary, the new subspecies is distinguished from A. crenata subsp. crenata by its lamina texture, shape of apex and sepal and from A. crenata subsp. obtusifolia by its lamina texture, shape and margin (Figs 1 , 2 ).

Zhang et al. (2007) examined the pollen grains of 23 species of Ardisia subgen. Crispardisia from China. The pollen grains of the studied taxa are subspheroidal to suboblate in shape and 3 - colporate, forming syncolpate (except for A. faberi ). Four pollen grain types were identified: type I (with foveolate-reticulate sculpture), type II (with finely reticulate sculpture), type III (with rugulate sculpture) and type IV (with finely granulate sculpture with spines). The pollen grains of A. crenata (based on the two samples of A. crenata , not identified at the infraspecific level) and one sample of A. crassinervosa E. Walker ( subsp. crassinervosa ) are classified as types I. Similar to these two studied taxa, the new subspecies has type I of pollen grain sculpturing. Additionally, the new subspecies are distinct amongst the most studied Ardisia taxa in terms of having tricolpate pollen with separate apertures at the pollen pole. Based on this pollen morphology, our collection is best recognised as a new subspecies of A. crenata , though studies on pollen morphology and other taxonomic characteristics are needed for further clarification of its taxonomic status.

Figures

Figure 1. Ardisia crenata subsp. mukdahanensis A, B habit C inflorescence D infructescence (Image by Wannachai Chatan).

Figure 2. Ardisia crenata subsp. mukdahanensis A leaf, adaxial side B leaf, abaxial side C intramarginal vein showing the distance from the margin D peduncle E flower bud F flower bud with corolla removed G dissected calyx, adaxial side H dissected calyx, abaxial side.

Figure 3. Ardisia crenata subsp. mukdahanensis A dissected corolla B corolla-lobe, adaxial side C corolla-lobe, abaxial side D androecium, adaxial side E androecium, abaxial F androecium with opened anthers, adaxial G gynoecium H dissected ovary showing the ovules (X. S.).

Figure 4. Ardisia crenata subsp. mukdahanensis A fruits, lateral view B fruits, bottom view C fruit’s surface showing its colour and lacks glandular punctation D – F seed, lateral, aerial and bottom views, respectively.

Figure 5. Distribution of Ardisia crenata subsp. mukdahanensis at Dong Luang District, Mukdahan Province, Thailand.

Figure 6. Scanning electron microscopy (SEM) photomicrographs of pollen morphology of Ardisia crenata subsp. mukdahanensis A, B show the pollen’s morphology at different magnifications.