Phtheirospermum lushaiorum R. Sengupta & S.S. Dash

Sengupta, Rabishankar & Dash, Sudhansu Sekhar, 2024, A new species of Phtheirospermum (Orobanchaceae) from Mizoram, an Indo- Burma biodiversity hotspot in India, Phytotaxa 645 (2), pp. 172-178 : 173-177

Phtheirospermum lushaiorum R. Sengupta & S.S. Dash , sp. nov.

( Figs 1 , 2 )

Diagnosis

Phtheirospermum lushaiorum is closely allied to Ph. tenuisectum Bureau & Franch. (1891:129) but differentiated by shorter height of 15– 22 cm, lobed pinnae, entire margin of the sepal, didynamous stamen, equally bilobed ovary.

Type. INDIA. Mizoram: Lawngtlai district,near Far Pak , Phawngpui National Park , 22°41'26.82"N, 093°02'34.68"E, 1967 m a.s.l., 18 September 2021, R. Sengupta & S.S. Dash 92715 (holotype CAL, barcode CAL0000253937 ; isotype CAL, barcode CAL0000253938 ) .

Perennial, erect herbs, 15–22 cm high, stem quadrangular, solid, erect, rarely branched, woolly pubescent, glandular, glandular hairs 0.8–1.1 mm, roots numerous, profusely branched, up to 0.5 mm thick, with haustoria at the place of contact with the host roots and developing many adventitious buds. Internodes 1.2–2.2 cm long, upper half of stems with shorter internode than lower half, brownish–green. Petioles 1 mm long, terete, densely pubescent, greenish. Leaves opposite; lower leaves sub-coriaceous, leaf blade triangular–ovate, 1.4–1.6 × 1.3–2.1 cm, pinnatisect; pinnae lobed, with multicellular villous 0.7–1 mm long glandular hair on both sides, apex mucronate sometimes cuspidate, dorsal side dark green, pubescent along veins; ventral side light green, densely pubescent with glandular hairs along veins. Inflorescence lax racemes. Flowers solitary, axillary from upper leaves, pedicellate, pedicel short, 1–2 mm long, slender, pubescent. Calyx persistent, tube ovate–oblong, obliquely cupular, 4–6 mm, densely pubescent, sparsely glandular villous; strongly 5–grooved, lobes lanceolate, 1.5–2.5 × 0.8–1 mm, equal, margin entire, dark green, erect, broadly triangular, margins densely ciliate, tips acute. Corolla tubular, 2-folded, yellow throughout, glandular on both side; tube 0.6–1.3 cm; throat pubescent; lower lobes obovate, 3-lobed, 3.5–5.5 mm, middle lobe slightly larger than two lateral lobes, orange stripes on the middle lip, lower lip margin ciliate, sparsely glandular, apex obtuse to obcordate; upper lobes triangular-ovate, 2-lobed, 2.5–3.5 mm. Stamens 4, didynamous, posterior stamens shorter than anterior stamens, included, filament 2–5 mm, terete, pubescent, hairs 0.5–1.0 mm; anthers woolly; anther locules 2, equal, distinct, parallel, basifixed, mucronate, dehiscing longitudinally. Ovary superior, densely pilose, narrowly ovoid, 0.4–0.6 mm long; style 1, 0.3–5 mm long; stigma bilobed, papillate. Capsule 4–6 mm, oblong, tip acute, with persistent style. Seeds 0.4 – 1 mm, many, ovoid.

Phenology

Flowering starts from July to September and fruiting from August to October.

Habitat and Ecology

Phtheirospermum lushaiorum grows as a hemiparasite in association with Swertia cordata Wall. , Potentilla gerardiana Lindl. , Argentina lineata (Trevir.) Soják and Smithia ciliata Royle. in Far Park (1967 m) grasslands. Few populations were also observed in open hill slopes, margins of montane Pine forests, moist areas in valleys; occurring in the altitudinal range from 1700 to 2100 m.

Distribution

Phtheirospermum lushaiorum was only recorded from the type locality ( Fig. 3 ). The species could not be located in any other areas in Mizoram during our study.

Etymology

The specific epithet “ lushaiorum ”is named after the“Lushai”tribe of Mizoram.The specific epithet honours the traditions and cultural heritage of the Lushai tribe of Mizoram for their commitment towards biodiversity conservation.

Other specimen examined

INDIA, Mizoram: Lawngtlai district, near Far Pak, Phawngpui National Park, 22°41’26.82”N, 093°02’34.68”E, 1967 m a.s.l., 18 September 2021, R. Sengupta & S.S. Dash 92715 (iso, CAL, barcode CAL0000253938); Lawngtlai district, near Vawmbuk, Phawngpui National Park, 22°40’15.9”N, 093°02’45.72”E, 1903 m a.s.l., 21 September 2021, R. Sengupta & S.S. Dash 71446 (para, CAL, barcode CAL0000253930).

Conservation status

Phtheirospermum lushaiorum , presently shows a restricted distribution at the type locality in Phawngpui national park (Far Pak) and dwindling in its natural habitat due to both anthropogenic and natural threats. The type locality of Phtheirospermum lushaiorum is near to Far Pak, which was reported to be highly affected by invasion of Ageratina adenophora , habitat destruction by forest fire, and clearing of forest for trail cleaning drives ( Sengupta & Dash 2020). Only one small population with four subpopulations of Phtheirospermum lushaiorum were found in and around the type locality in Far Pak (1700-2100 m) area of Phawngpui national park in Mizoram. Additionally, the known subpopulations are severely fragmented and distributed in an interrupted manner. The observed known co-ordinates of occurrence were plotted using GeoCAT (Source: https://geocat.kew.org) online mapping tool to assess the Extent of Occurrence (EOO) and Area of Occupancy (AOO) ( Bachman et al., 2011). Each subpopulation exhibited 15–37 mature individuals along with very few young individuals in an interrupted manner across altitudinal gradient which were studied during the study period of three years (2019–2021). The area of occupancy (AOO) (based on a grid extent of 2× 2 km 2) was determined to be 8.00 km 2, whereas the extent of occurrence (EOO) was assessed to be 4.546 km 2 ( Figure 3 ), both being <10 km 2. Therefore, based on the present occurrence records and observations, the area of occupancy (AOO) and numbers of known population and its subpopulations, the threat perception of the taxon is assessed as Critically Endangered under Criteria C [CR CC2a(i+ii)] of IUCN guidelines (2022).

Taxonomic note

Phtheirospermum lushaiorum is similar to Ph. tenuisectum in its floral colour, quadrangular stem, lax racemes and oblong-ellipsoid capsule. Morphological differences between these two species are mentioned in Table 1 . Phtheirospermum lushaiorum can be distinguished from all other species under the genus Phtheirospermum in having unbranched stem, didynamous stamens, lobed pinnae in pinnatisect leaves and entire calyx margin ( Figure 1 ). Corolla of Phtheirospermum lushaiorum are yellow throughout in both upper and lower lip as compared to other species of Phtheirospermum where the upper lip is with yellow reddish tinge ( Figure 2 ).

Figures

FIGURE 1. Phtheirospermum lushaiorum R. Sengupta & S.S. Dash.(A) Habit; (B) Lateral view of flower; (C) anterior view of flower;(D) Leaf; (E) corolla split open; (F) stamens; (G) pistil with calyx split open; (H) fruit;(I) Seed.

FIGURE 2. Phtheirospermum lushaiorum R. Sengupta & S.S. Dash. (A) Habitat; (B) Habit; (C) Close up of flowers;(D) side view of flower; (E) leaf; (F) internode; (G) buds; (H) front view of flower; (I) fruits.

FIGURE 3. Threat assessment map of Phtheirospermum lushaiorum R. Sengupta & S.S. Dash in its occurrence sites in Mizoram, India.