Peliosanthes linearifolia Kroupsky, N.Tanaka, K.S.Nguyen & Nuraliev, 2023

Kroupsky, Ivan A., Lyskov, Dmitry F., Nguyen, Khang Sinh, Pham, Thoa Kim Thi, Nguyen, Cuong Huu, Kuznetsov, Andrey N., Kuznetsova, Svetlana P., Vislobokov, Nikolay A., Tanaka, Noriyuki & Nuraliev, Maxim S., 2023, Peliosanthes linearifolia (Asparagaceae), a new species with linear leaves from Vietnam, Phytotaxa 607 (1), pp. 95-104 : 96-102

Peliosanthes linearifolia Kroupsky, N.Tanaka, K.S.Nguyen & Nuraliev , sp. nov. ( Figs 1–4 )

Diagnosis: — Peliosanthes linearifolia differs from most of its congeners in linear to narrowly lanceolate leaf blades that are not more than 1.1 cm wide. It belongs to the P. teta species group, but constantly possesses single flowers in axils of primary bracts, unlike the other members of the group. The new species is most similar to P. graminea , differing additionally in leaf blades not more than 22 cm long and in violet flowers.

Type: — VIETNAM. Quang Nam Province: Tay Giang District , A Xan Municipality, Lang Po Mu homestay area, disturbed forest on local ridge with Fokienia hodginsii and bamboo, 15°48’24’’N 107°19’52’’E, elev. 1320 m, 18 March 2022, Nuraliev M.S., Lyskov D.F. NUR 3457 (holotype: MW: MW0595833 !; isotypes: MW: MW0595834 !, MW0595835 !) .

Additional specimens examined (paratypes): — VIETNAM. Quang Nam Province: Tay Giang District , A Xan Municipality, Lang Po Mu homestay area, disturbed forest on local ridge with Fokienia hodginsii and bamboo, 15°48’22’’N 107°19’30’’E, elev. 1420 m, 18 March 2022, Nuraliev M. S ., Lyskov D. F. NUR 3463 ( MW: MW0595836 , MW0595837 , MW0595838 ) ; Quang Nam Province: Tay Giang District , A Xan Municipality, Lang Po Mu homestay area, primary evergreen broad-leaved forest mixed with Fokienia hodginsii along local ridge, around point 15.80671°N 107.33066°E, elev. 1300–1350 m, 19April 2022, Pham T. K. T ., Nguyen C. H ., Nguyen K. S ., Cao H .X. CKH 2022041919 ( HN; VNF).

Specimen in living collection: — Living plant from the same gathering as the type (Nuraliev, Lyskov NUR 3457 ), cultivated in the Main Botanical Garden of the Russian Academy of Sciences (Moscow), garden number: 2022.17296 .

Etymology: —The specific epithet refers to the linear leaf blades which distinguish the new species from virtually all its congeners.

Description:—Plant herbaceous, terrestrial, perennial, evergreen, entirely glabrous. Rhizome stoloniform, decumbent, at least 12 cm long, 1–2 mm in diameter, yellowish green; rhizome consisting of regions with long internodes, bearing cataphylls, alternating with regions with short internodes, bearing cataphyll(s) and 2 or 3 foliage leaves; apical portion with short internodes, erect, ca 2–3 cm long, bearing cataphylls, numerous foliage leaves and usually 1 or 2 inflorescences. Roots borne in nodes, few, poorly branched, 1.1–3.2 mm in diameter, rigid, greenish to yellow, densely covered with root hairs. Cataphylls up to 4.5 cm long, up to 7 mm wide, chartaceous, lanceolate, light brown, soon becoming dry; cataphylls on stoloniform portion of rhizome presumably much shorter, sheathing. Foliage leaves ascending, simple, stiff. Petiole adaxially flattened, 4.5–9.5 cm long, 0.6–1.7 mm in diameter. Leaf blade entire, linear to narrowly lanceolate (or ensiform), 13–22 cm long, 6–11 mm wide, 10–30 times as long as wide, dark green; base narrowly cuneate; blade gradually tapering towards apex but apex itself obtuse; margin entire, canaliculate along lateral edge and scabrous (visible under magnification); longitudinal veins 5 (including midvein, showing basal perfect acrodromous venation), parallel; transversal veinlets numerous, hardly visible, sub-perpendicular to longitudinal veins. Inflorescence a lax raceme (i.e., flowers solitary in axils of primary bracts), erect to ascending, up to ca 16 cm long. Peduncle erect, 3–5.5 cm long, ca 1–1.5 mm in diameter, longitudinally ribbed, violet, bearing 2 or 3 sterile bracts; sterile bracts 9–10 mm long, 2–2.5 mm wide, scarious when mature, indistinctly unicostate, navicular, lanceolate, violet. Rachis straight to arcuate, up to 10.5 cm long, longitudinally ribbed, violet, bearing up to 26 flowers. Flowersubtending bracts 4–6 mm long, 3 mm wide, scarious when mature, indistinctly unicostate, navicular, lanceolate, violet. Flowers sparsely arranged, actinomorphic, bisexual, facing horizontally to slightly nodding, generally dark violet to brownish violet. Pedicel 3 mm long, 0.8–1 mm in diameter, articulated with ovary. Bracteole single, transversal, 3–4 mm long, 0.5–1 mm wide, smooth, ovate. Perianth rotate, homochlamydeous, 7–8 mm in diameter when fully opened; lobes 6, arranged apparently in two similar whorls with imbricate-alternate aestivation (in bud), at anthesis outer lobes slightly overlapping inner lobes; lobes subequal, 3 mm long, 2–2.5 mm wide at base, trullate or ovate, with rounded apex, with irregularly repand margin, horizontally spreading, sometimes slightly recurved, dark violet and usually with brownish central stripe on both sides becoming more distinct in old flowers. Stamens 6; filaments united forming fleshy corona-like structure (so-called corona); corona 1.5–1.8 mm high, 3.2–3.9 mm in diameter, broadly dome-shaped and hexagonal in outline, apically with 6 prominent broadly triangular lobes in the radii of anthers, dark violet and sometimes greenish especially along tepal bases; orifice of corona 1.7–2.0 mm in diameter; anthers in the radii of tepals, attached to the inner surface of corona just below orifice, dorsifixed, introrse, sessile, 1 mm long, cylindrical to ovate, light purple, longitudinally dehiscent. Ovary inferior, broadly obconical, 1.5 mm high, 1.5–2 mm wide in upper part, 3-locular, each locule bearing 4 ovules; style 1.5–1.8 mm high, 0.7–1 mm wide at base, narrowly conical with prominent furrows along borders between carpels; stigmas 3, carinal, less than 0.5 mm long, occupying apical surface of style and not prominent beyond style width, verrucose. Seeds unknown.

Phenology: —Flowering from March to April.

Distribution and ecology: — Peliosanthes linearifolia is currently only known from a single forest area in Tay Giang District (Quang Nam Province, Vietnam), where the type and the paratypes were collected along a local mountain ridge c. 700 m long. The new species is rather common within the ridge at elevations of 1300–1450 m a.s.l. The forest area is remarkable for a dense population of the conifer Fokienia hodginsii A.Henry & H.H.Thomas (Cupressaceae) . The mountain ridge where P. linearifolia was discovered is particularly rich in huge trees of F. hodginsii .

The known population of P. linearifolia is located about 6 km from the Vietnam-Laos border, not far from Xe Xap National Bio-Diversity Conservation Area in Laos, where the species can potentially also occur.

Within the local mountain ridge, P. linearifolia co-occurs with Cryptostylis arachnites (Blume) Hassk. , Didymoplexis gibbosa Aver. & Nuraliev , Trichotosia microphylla Blume (Orchidaceae) , Calamus rhabdocladus Burret (Arecaceae) , Rhopalocnemis phalloides Jungh. (Balanophoraceae) , Myrsine stolonifera (Koidz.) Walker (Primulaceae) (see also Averyanov et al. 2022). In addition, the ridge is inhabited by a dense population of a bamboo Bambusa sp. (Poaceae) .

Taxonomic relationships: —The species described here undoubtedly belongs to the genus Peliosanthes ( Jessop 1976, 1979, Chen & Tamura 2000, Tanaka 2018) as far as it exhibits the following morphological traits: perennial evergreen terrestrial rhizomatous herbaceous habit; petiolate leaves; rigid leaf blade with characteristic basal perfect acrodromous venation of several prominent parallel veins and numerous transversal veinlets; above-ground shoots with few inflorescences, trimerous flowers with a corona-like structure bearing sessile anthers.

The new species is readily distinguished from most of its congeners by the following combination of morphological features: stoloniform rhizome, lax inflorescence, rachis of equal thickness with peduncle, flowers pedicellate and facing horizontally to slightly nodding, widely open perianth, and inferior ovary.

We assign the new species to the Peliosanthes teta species group, which is mainly characterized by lax thyrse with flowers solitary or clustered by 2–5 in the axils of the bracts; pedicellate, horizontally facing flowers; widely open (often rotate) perianth; androecial corona not divided into lobes or shortly lobed; inferior or semi-inferior ovary; short thick style (Tanaka 2004, see also Table 1 ). Although P. linearifolia , unlike all the previously known species of P. teta group, uniformly possesses single flowers in axils of primary bracts, we found the overall similarity of P. linearifolia to all its known members substantial enough to consider this species a part of P. teta group. An additional argument here is the unusual shape of leaves in the new species, which is unknown outside the P. teta group (see below).

Peliosanthes teta group includes P. divaricatanthera N.Tanaka (2004: 157) , P. graminea Ridley (1911: 207) , P. minor Yamamoto (1943: 29) , P. teta Andrews (1810 : t. 605), P. tonkinensis F.T. Wang & Tang (1936: 83) and P. torulosa Y. Wan (1986: 147) . The species limits within this group are rather complicated, and views of different authors on this issue are controversial. For example, P. minor , P. tonkinensis and P. torulosa were treated as synonyms of P. teta in Flora of China ( Chen & Tamura 2000), and a close similarity of P. graminea with P. teta was pointed out along with its description by Ridley (1911); these four species were merged within P. teta by Govaerts et al. (2023). Here, we follow a narrow circumscription of P. teta proposed by Averyanov et al. (2021). More precisely, Averyanov et al. (2021) assigned only those specimens to this species that closely meet its protologue and the type drawing ( Andrews 1810). We also follow Tanaka (2004) in accepting P. minor , P. tonkinensis and P. torulosa as distinct species, considering at the same time that the knowledge on morphology and variation of these three species is still poor.

The main morphological differences between P. linearifolia and the other species of P. teta group are summarized in Table 1 . Apart from the uniformly racemose inflorescences mentioned above (i.e. those with single flower in axil of each primary bract), the new species differs from the other ones, except for P. graminea , in linear to narrowly lanceolate leaf blades up to 1.1 cm wide. In P. divaricatanthera , P. minor , P. teta , P. tonkinensis and P. torulosa the leaf blades are at least 2 cm wide. Peliosanthes linearifolia further differs from P. graminea , a poorly known species currently documented only from the Malay Peninsula ( Ridley 1911), in leaf blades 13–22 cm (vs 30–36 cm) long, and in violet (vs green) flowers. An additional remarkable feature of P. linearifolia is the prominently lobed corona apex, which is also present in P. torulosa , whereas P. divaricatanthera and P. teta are characterized by circular to hexagonal apical margin (orifice) of corona; this character remains unknown in the rest of the species.

The stoloniform rhizome of P. linearifolia makes this species similar in its life form with P. minor and P. torulosa , and different from P. teta var. angustifolia Ridley (1911: 207) , the latter taxon being indicated to possess short rhizome by Ridley (1898).

Finally, the linear (approaching narrowly lanceolate) leaf blades that are not more than 1.1 cm wide are among the most important diagnostic characters of the newly described species, since they are extremely rare in the entire genus Peliosanthes . Indeed, leaves of similar shape and width were previously known only in P. graminea , whereas the vast majority of the species of Peliosanthes are characterized by oblong, lanceolate or elliptic blades ( Chen & Tamura 2000). Several other species possess narrowly lanceolate or narrowly elliptic leaf blades, e.g. P. laotica Vislobokov, Nuraliev & N.Tanaka in Vislobokov et al. (2023), P. ophiopogonoides F.T.Wang & Tang in Wang et al. (1978: 253) ( Chen & Tamura 2000), P. pumila N. Tanaka (2019: 298) , P. triandra Aver. & N.Tanaka in Averyanov et al. (2014: 18), P. yunnanensis F.T.Wang & Tang in Wang et al. (1978: 254) ( Chen & Tamura 2000). In all these cases, leaf blades are wider than 1.3 cm (sometimes much wider), being still significantly different in this respect from P. linearifolia and P. graminea .

Figures

FIGURE 1. Peliosanthes linearifolia. A, B. Plant in natural habitat. Nuraliev, Lyskov NUR 3457. Photos by M.S. Nuraliev.

FIGURE 2. Peliosanthes linearifolia, general morphology. A.Above-ground shoot with two inflorescences (side view). B. Apical portion of rhizome with bases of leaves and inflorescence (side view). C. Leaf blade, abaxial side. D. Inflorescence (side view). E. Portion of inflorescence showing flowers at different stages of anthesis. Nuraliev, Lyskov NUR 3457 (A–C, E) and Nuraliev, Lyskov NUR 3463 (D). Photos by M.S. Nuraliev.

FIGURE 3. Peliosanthes linearifolia, floral morphology. A. Flower (lateral view). B, C. Flowers at the very beginning anthesis and at late anthesis (front views). D, E. Flowers (semi-side views). F. Corona, anthers and style (front view). G, H. Longitudinal sections of flowers. Nuraliev, Lyskov NUR 3457 (B–D, H) and Nuraliev, Lyskov NUR 3463 (A, E–G). Photos by M.S. Nuraliev.

FIGURE 4. Peliosanthes linearifolia, fixed plants. A. Flattened alcohol-fixed plant (Pham et al. CKH 2022041919, photo by K.S. Nguyen). B, C. Bases of dried plants, showing stoloniform rhizome (Nuraliev, Lyskov NUR 3463, photos by M.S. Nuraliev).