Isodon xiaoluzhiensis Huan C. Wang & Shi Gang Li, 2024

Li, Shi-Gang, Huang, Qiang-Chun, Liu, Shao-Yun, Xiang, Chun-Lei & Wang, Huan-Chong, 2024, Isodon xiaoluzhiensis (Lamiaceae, Nepetoideae), a new species from Yunnan, southwest China, PhytoKeys 237, pp. 191-200 : 191

Isodon xiaoluzhiensis Huan C. Wang & Shi Gang Li sp. nov.

Figs 1 , 2 , 3 , 4

Type.

China. Yunnan Province: Yimen County, Luzhi Town, Xiaoluzhi village , Maomao Mountain , on limestone grasslands, 24°40'N, 101°57'E, alt. 1300-1400 m, 18 January 2018, H. C. Wang et al. YM8034 (Holotype: YUKU!; isotype: YUKU!, PE!, KUN!) .

Diagnosis.

Isodon xiaoluzhiensis is most similar to I. adenanthus (Diels) Kudô in having similar flower shape, but it clearly differs from the latter in its procumbent (vs. erect or ascending in I. adenanthus ) habit, stems and branches woody (vs. non-woody) with densely white glandular puberulent (vs. densely retrorse gray pubescent), leaves usually narrowly ovate to rhomboid, rarely lanceolate (vs. rhombic-ovate to ovate-lanceolate), small, 0.8-1.4 cm long (vs. 1.5-6.5 cm long), 0.2-0.5 cm wide (vs. 1.0-2.5 cm wide), teeth of calyx subobtose to subacute (vs. apiculate) at apex, posterior lip of corolla non-spotted (vs. purple spotted). Additionally, I. xiaoluzhiensis flowers from November to January, nevertheless I. adenanthus usually flowers from March to August.

Description.

Small shrubs or subshrubs. Stems woody, procumbent, branched; branches subterete to terete, usually grey, irregularly decorticate, glabrescent; branchlets obtusely quadrangular, purplish, densely white glandular-puberulent. Leaves opposite; petiole 1-3 mm long, rarely subsessile; leaf blades papery or thinly coriaceous, usually narrowly ovate to rhomboid, sometimes lanceolate, 0.8-1.4 cm long, 0.2-0.5 cm wide, apex acute, base cuneate to narrowly cuneate, adaxial surfaces green in young leaves, purplish black when ageing, with pellucid glands, abaxial surfaces gray-green, densely white glandular-puberulent; margin coarsely serrated, with 1-4 teeth on each margin, sometimes entire; veins adaxially depressed, abaxially prominent, with coarse short white hirsute puberulent, lateral veins 2-3 paired. Inflorescences terminal racemose or paniculate, composed of dichasial cymes. Peduncles of cymes gracile, 4-5 mm long, white glandular-puberulent; lax usually with 3-5 flowers; bracts ovate small, subsessile. Flowers small, pedunculate; pedicels gracile, with white glandular-puberulent, 4-5 mm long. Calyx campanulate, conspicuously 10-veined, densely white hirsute outside, 2-3 mm long, 2.0-2.5 mm wide, inconspicuously 2-lipped; posterior lip 3-toothed, subequal, ovate, ca. 1 mm long, usually subobtuse to subacute at apex; anterior lip 2-toothed, equal, ovate, 1.0-1.2 mm long, subobtuse at apex; tube declinate, usually 2 mm long. Corolla purple or light purple, bilabiate, 4-5 mm long; tube tubular, geniculate at base, ca. 2 mm long, densely pubescent outside; posterior lip strongly reflexed, 4-lobed, apex round; anterior lip concave, navicular, obviously longer than the tube, 2.5-3.0 mm long. Stamens 4, didynamous, exserted, inserted at bottom of corolla tube; filaments slender, white villous at base, 5-6 mm long; anthers bluish-purple, elliptic, versatile. Pistil 1, style exserted,7-8 mm long, slightly longer than filaments; ovary superior. Nutlets nearly ovoid, glabrous, sparsely glandular.

Phenology.

Flowering from November to January, fruiting from December to February.

Etymology.

The specific epithet " Isodon xiaoluzhiensis " is derived from the type locality of the new species, the Xiaoluzhi village, and the Latin suffix - ensis, indicating the place of origin or growth.

Vernacular name.

Chinese mandarin: xiao lu zhi xiang cha cai (小绿汁香茶菜).

Distribution and ecology.

According to the present investigations, I. xiaoluzhiensis is only found in its type locality, i.e. Xiaoluzhi village of Luzhijiang valley, Yimen County, Yunnan Province, southwest China, where the climate is seasonally hot and arid. Isodon xiaoluzhiensis occurs in the limestone grasslands between 1,300 m and 1,400 m elevation. In the type locality, its association mainly includes Dodonaea viscosa (L.) Jacq. ( Sapindaceae ), Indigofera vallicola Huan C.Wang et Jin L. Liu ( Leguminosae ) (a new species discovered by Liu et al. (2022)), Duhaldea lachnocephala Huan C. Wang et Feng Yang ( Compositae ) (an endemic species of Luzhijiang valley discovered by Yang et al. (2022)), Selaginella pulvinata (Hook. et Grev.) Maxim ( Selaginellaceae ), Pterygiella luzhijiangensis Huan C. Wang ( Orobanchaceae ) and Onosma decastichum Y. L. Liu ( Boraginaceae ). Among them, the type localities of I. vallicola , D. lachnocephala , P. luzhijiangensis , O. decastichum are also in Xiaoluzhi of the Luzhijiang valley ( Qiao et al. 2018; Liu et al. 2022; Yang et al. 2022).

Preliminary conservation status.

Isodon xiaoluzhiensis is a rare species with a restricted distribution and small population size. It is only known from in the upstream region of the Luzhijiang River in the Yimen county, which is no protected area covering. The total population size is estimated at less than 50. According to the IUCN Standards and Petitions Subcommittee (2019), this new species should be considered as "Critically Endangered" (CR).

Additional specimens examined

(paratypes): China. Yunnan: Yimen County, Luzhi town, Xiaoluzhi village , Maomao Mountain , elev. ca. 1390 m, 25 Sep. 2021, H. C. Wang et al. YM14638 (YUKU) .

Discussion.

Isodon xiaoluzhiensis exhibits all the characteristics of Isodon , but having a procumbent habit, relatively small leaves, and the phenology of flowering in winter can easily differentiate it from other species in the genus. Especially, the procumbent habit is rare in the entire genus Isodon , just I. xiaoluzhiensis and I. hsiwenii , nevertheless the latter is sometimes arcuate. Isodon xiaoluzhiensis is very similar to I. adenanthus (Diels) Kudô in terms of flower shape and size, but it clearly differs from the latter by its stem woody (vs. non-woody), procumbent (vs. erect or ascending), highly (vs. sparsely) branched, densely white glandular puberulent (vs. densely retrorse gray pubescent), leaves usually narrowly ovate to rhomboid (vs. rhombic-ovate to ovate-lanceolate), papery or thinly coriaceous (vs. herbaceous), small, 0.8-1.4 cm long (vs. 1.5-6.5 cm long), 0.2-0.5 cm wide (vs. 1-2.5 cm wide), teeth of calyx subobtuse to subacute (vs. apiculate) at apex, posterior lip of corolla non-spotted (vs. purple spotted).

Isodon xiaoluzhiensis is somewhat close to I. hsiwenii Y. P. Chen et C. L. Xiang in sharing relatively small leaves and procumbent stems. However, I. xiaoluzhiensis diffeers from I. hsiwenii by its main stems up to 60 cm long (vs. up to 100 cm for I. hsiwenii ), leaves adaxially green or purplish black with pellucid glands (vs. dark green, densely puberulent and colorless glandular), leaves abaxially gray-green and densely white glandular-puberulent (vs. light green, densely puberulent colorless glandular on both sides), calyx purple with few green (vs. green outside), veins densely white hirsute outside (vs. densely purplish puberulent on veins), calyces teeth at apex subobtuse to subacute (vs. acute). Additionally, the habitats of these two species are distinctly different and non-overlapping. Isodon hsiwenii is only known from northeast Yunnan, situated in Jinshajiang River basin, and grows on stony slopes at an altitude of approximately 1 750 meters. Conversely, I. xiaoluzhiensis is discovered in Central Yunnan, located within the Honghe River basin, and inhabits the limestone grasslands between 1300 m and 1400 m at elevation. A morphological comparison of I. xiaoluzhiensis with I. adenanthus and I. hsiwenii is provided in Table 1 .

Figures

Figure 1. Isodon xiaoluzhiensis sp. nov. A habit B flower (side view) C calyx D corolla (vertical view) E style and stamens.

Figure 2. Holotype of Isodon xiaoluzhiensis (YUKU- 05008415).

Figure 3. Isodon xiaoluzhiensis sp. nov. A, B habit C perennial stem D branchlet E adaxial surface of leaf F abaxial surface of leaf G-I inflorescence J corolla (front view) K flower (lateral view) L corolla (rear view) M calyx.

Figure 4. Isodon xiaoluzhiensis sp. nov. A adaxial surface of leaf B abaxial surface of leaf C flower (lateral view) D flower without calyx E calyx F pistil and stamens.