Isodon maoershanensis R.H.Jiang & Jian L.Li

Li, Jian-Ling, Tang, Zhong-Xiang, He, Qiu-Lan, Wang, Shao-Neng, Liang, Sheng-Hua & Jiang, Ri-Hong, 2024, Isodon maoershanensis (Lamiaceae), a new species from Guangxi, South China, Phytotaxa 645 (1), pp. 91-97 : 92-94

Isodon maoershanensis R.H.Jiang & Jian L.Li , sp. nov. ( Figure 1 )

Type: China, Guangxi, Guilin City, Xing’an County , Mao’er Mountain National Nature Reserve , 25°51′58.51″N, 110°24′44.16″E, 2065 m a.s.l., 9 September 2023, 20230909002 (Holotype: GXFI!, Isotype: GXFI!).

Diagnosis

The new species is most similar to I. henryi (Hemsl.) Kudô (1929: 123) ( Li & Hedge 1994), and the similarities are that the panicle is composed of 3–5 flowers, the calyx and corolla are covered with hairs and glandular points, and the style and stamen are hidden. But there are obvious differences between the two, which are: the leaf of the new species is covered with dense white short stiff hairs and scattered glandular points above, at the back is covered with dense red glandular points, and covered with short stiff hairs along the veins [vs the latter: the leaf is densely covered with strigose above, and the back is sparsely covered with strigose along the veins]; the peduncle of the cymes is covered with short stiff hairs and red glandular points (vs covered with glandular pubescence); the crown apex is 1/ 4 type 2- lip shape, the upper lip has 4 flat petals, and the outside is covered with short stiff hairs, jointed long hairs and red glandular points (vs the upper lip is 3/ 2 type 2-lip shape, the upper lip has 3 reflexed petals, and the outside is covered with short pubescence and glandular points, with purple spots).

Isodon maoershanensis is also similar to I. megathyrsus (Diels) H.W. Li (1988: 374) ( Wu et al. 1977), such as both leaves are hard papery, the length of the corolla tube is about 5 mm, the base is shallow sac-shaped, the corolla is covered with hairs and glandular points, and the lower lip is boat-shaped, the style and stamen are hidden, but the differences between the two are: the former panicle is 8–20 cm long, the cyme has 3–5 flowers, and the peduncle is 2–13 mm long (vs the latter’s panicle is wide, up to 20× 30 cm, the cyme has 5–11 flowers, and the peduncle is 5–35 mm long); pedicels and calyx sparsely stiff hairs and red glandular points (vs dense glandular pubescent); corolla white or pale purple, ca. 4 mm long, sparsely stiff hairs and red glandular points (vs blue or blue-purple, ca. 9 mm long, sparsely pubescent and glandular points). From the morphological characteristics, the new species is most distinctly different from its known relatives by the dense red glandular points on almost the whole plant.

A comparison of morphological characteristics of I. maoershanensis and the two most similar species is listed in TABLE 1 .

Description:—Perennial herbs; stems erect, 30–50 cm tall, quadrilateral, ribbed with shallow grooves, ribbed with very short white microvillus. Except main stem of plant, the leaves, bracteal leaves, bracts, peduncle, pedicel, calyx and corolla are covered with white microvillus and red glandular points. Leaves simple and opposite, hard papery, triangular-ovate or rhomboid-ovate, 2.0–4.0×1.2–3.0 cm, apex acuminate, base abruptly contractive below middle or subtruncate, downward into pseudo-petioles with gradually narrow long wings, margins crenate except base, crenate apex with callosum; leaves adaxially green, densely covered with white short stiff hairs and scattered glandular points, abaxially light green, full covered with red glandular points, along veins covered with white short stiff hairs. Petioles 0.5–2.0 cm long, short or almost sessile toward upper stem branches; the lateral veins are arcuate, 3–4 pairs, visibly dented above and protruding below. Panicle terminal on main and lateral branches, 8–20 cm long, consisting of cymes; the cyme has 3–5 flowers, peduncles 2–3 mm long, pedicels conspicuous, 2–4 mm long, both peduncles and pedicels are covered with very short stiff hairs and red glandular points. Bracteal leaves foliate, rhomboid, with short petiole, bracts and bracteoles elliptic or broadly lanceolate, small, ca. 4 mm long. Calyx broadly funnel-shaped when flowered, ca. 2 mm long, purplish or dark red, outer covered with white stiff hairs and red glandular points, calyx lobes 5, 2-lipped, split to 1/2 of calyx tube or less, upper lip 4 lobes smaller; calyx when fruiting conspicuously elongated, 4–5 mm long, distinctly veined, slightly paler in color, with stiff hairs and glandular points, slightly curved. Corolla white or pale purple, ca. 5 mm long, outer covered with stiff hairs and glandular points, inner glabrous; corolla tube ca. 5 mm long, outside with short stiff hairs, shallowly sacculate near base, ca. 2 mm wide to throat; corolla limb 2-lipped, upper lip flat, ca. 3 mm long, apex 4-lobed, round or truncated, lower lip broadly ovate, ca. 3mm long, concave, navicular. Stamens 4, recessed, 6–8 mm long, filaments flattened, white hairs below middle. Style sub equal to stamens, stigma 2-lobed, not projecting out of corolla. Discoid annular. Nuts small, oblong, about 1.2 mm long, brown, glabrous. Flowering August to October, fruiting September to November.

Phenology: —Flowering in August to October and fruiting in September to November. The new species was collected with flowers and young fruits in September.

Distribution and habitat: —The new species is found in subtropical evergreen broad-leaved forest. At present, only one occurring site has been found. The population grows well. It grows in the rocky seam, with high humidity, high wind and low temperature, at about 2065 m a.s.l.

Mao’er Mountain Nature Reserve is located in Guilin City in the northeast of Guangxi in south China. The terrain of the reserve is complex and diverse, the climate is changeable, and there are obvious microclimate phenomena, the temperature is obvious different among the top of the mountain, the foot of the mountain and the valley, sometimes the temperature difference can reach 10℃~ 14℃. The microclimate phenomenon leads to a high species diversity in the protected area, and we suspect that it also enhances the possibility of new species to some extent ( Shi et al. 2023, Bueno et al. 2021).

Conservation status: —The new species is currently known for a single site. The population grows well, but further in-field research is necessary for identifying possible threats, evaluating the population size and dynamic, and assessing the correct conservation status of the species according to the IUCN (2022). In fact, newly described species are initially often known from a single locality, but they are attributed to very different threat categories, such as Critically Endangered (CR) ( Wagensommer & Venanzoni 2021), Vulnerable (VU) ( Swanepoel et al. 2021), Near Threatened (NT) ( Perrino et al. 2018), Data Deficient (DD) ( Chinchilla 2020).

Etymology: —The epithet “maoershanensis ” refers to the locus classicus, Mao’er Mountain National Nature Reserve, whose pronunciation is “mao’er shan” in Chinese .

Figures

FIGURE 1. Isodon maoershanensis R.H.Jiang & Jian L.Li: A. Habit; B. Flowering branch; C. The two sides of leaf; D. Inflorescence; E. Front view of flower; F. Side view of flower; G. Flower anatomy; H. Leaf shapes; I. Adaxial side of leaf; J. Abaxial side of leaf. Photographed by Jian-Ling Li.