Arisaema longitubum Z.X. Ma, 2018

Ma, Zheng-Xu, 2018, Arisaema longitubum (Araceae), a new species from northwestern Yunnan, China, Phytotaxa 358 (3), pp. 295-299 : 295-299

Arisaema longitubum Z.X. Ma , sp. nov. ( Figs. 1 , 2 )

This species is closely related to Arisaema yunnanense Buchet and A. lidaense J. Murata & S.K. Wu , but differs from both in having a broadly ovate or subrhombic central leaf blade, pure olive-green spathe, a long cylindric spathe tube, a light green to transluscent and auriculate throat with olive-green reticulations, laxly arranged pistils and a suberectinward spadix-appendix.

Type:— CHINA. Yunnan Province: Lijiang City, Yulong County, Jin’an Township , Dangniuluo , ca. 2,630 m, 28 July 2015, Zhengxu Ma 003 (holotype PE!, isotypes, HUH!, PE!) ;

Perennial herb, seasonally dormant, paradioecious. Subterranean stem tuberous, subglobose, 2.0–3.0 cm in height, 2.0–5.0 cm in diam. Cataphylls 2, reddish brown to maroon, membranous, to 20.0 cm in length. Leaf solitary; petiole reddish brown to maroon or olive-green, smooth, 25.0–32.0 cm in length, 0.5–0.7 cm in diam., forming a pseudostem proximally; leaf blade dull green, hastate when juvenile, trifoliolate or sometimes coalesce at base when mature, sub-leathery; veins abaxially raised, lateral numerous; central leaflet broadly ovate or subrhombic, 10.0–11.0 × 7.5–10.0 cm, base sessile, apex nearly acuminate; lateral leaflets obliquely ovate, 9.5–11.0 × 6.4–8.0 cm, base sessile, apex nearly acuminate. Peduncle olive-green or reddish brown to maroon, smooth, to 40.0 cm in length. Inflorescence solitary, slightly higher than leaf. Spathe olive-green, unicolor, glaucous, smooth; tube cylindric, 5.5–8.0 cm in length, 1.0– 1.5 cm in diam.; mouth light green to translucent, with obvious olive-green reticulations, membranous, widening and slightly revolute; limb olive-green, flat, base light green, expanding, (3.2–)4.5–6.0 × (1.5–) 2.4–2.7 cm, apex acuminate. Spadix unisexual. Female zone cylindric, 2.3–3.0 × 0.4–0.6 cm; pistils lax arranged; ovary green, barrel- shaped; style white, cylindric, ca. 1.2 mm in length; stigma white, circular, pilose. Male zone cylindric, ca. 2.6 × 0.2 cm; synandria laxly arranged, pale yellow, stipitate, comprising 4 thecaes of each; thecae globose, dehiscing by an apical pore. Appendix green, sometimes dark purplish at apex, slender-cylindric, proximally sessile, distally slightly attenuate, incurved, 3.2–4.5 × 0.1–0.3 cm, slightly protruding the spathe mouth.

Phenology:— Flowering in July to August. Fruiting unknown.

Eponymy:— The epithet of this species, longitubum , refers to its obviously long cylindric spathe tube. Therefore, the author recommends the Chinese name of this new species as “łffifflfl”.

Distribution and habitat:— Arisaema longitubum is so far known only from two separate populations in Yulong county and Eryuan county. It grows as an understory herb in the secondary forest dominated by Alnus sp. , along roadsides and edges of grasslands at the boundary of the Jinshajiang dry-hot river valley. Habitats of this species are severely affected by human activities, especially land reclamation and laboring.

Discussion:— The morphological characteristics of Arisaema longitubum is consistent with characters identified for Arisaema sect. Odorata in having, (i) a tuberous subterranean stem producing numerous annularly arranged raised accessory buds; (ii) trifoliolate leaf blades; (iii) a slender cylindrical and slightly incurved spadix-appendix without the presence of neuter flowers; and (iv) barrel-shaped pistils.

Arisaema longitubum is closely related to A. yunnanense but differs in having (i) sub-leathery and subrhombic to broadly ovate central leaf blade; (ii) olive-green spathe—pale colored and narrow at basal portion becoming reticulate and widening towards the mouth; (iii) mouth margin slightly revolute; (iv) laxly arranged barrel-shaped pistils; (v) pale-yellow synandria; and (vi) a slender cylindrical spadix-appendix that slightly incurves distally.

Besides, A. longitubum differs from A. bathycoleum as the latter has (i) linear, unifoliolate or trifoliolate leaf blades; (ii) densely arranged spindle-shaped pistils; and (iii) a filiform and pendulous spadix-appendix occasionally twining distally.

In addition, A. longitubum is also similar to A. lidaense but distinct based on observations on the reproductive biology conducted in the field. Sexual reproductive phase of the former interchanges between male phase and female phase from one year to another, in contrast to the latter that only changes between male phase and monoecious phase. Apart from that, the white patch on the spathe-throat is also a diagnostic characteristic of the latter. From a biogeographical perspective, A. longitubum inhabits a relatively drier and cooler region, usually along the margin of the dry-hot river valley at higher elevation in northwestern Yunnan. Meanwhile, A. lidaense only grows in the limestone region, developing evergreen broad-leaf forest, in southeastern Yunnan to northeastern Vietnam ( Nguyen et al. 2016) where precipitation is considerably higher. More specific comparisons are listed below in Table 1.

Additional specimen examined (paratype):— CHINA. Yunnan Province: Dali Prefecture, E of Eryuan County, ca. 2570–2640 m, 31 August 2015, BjØrnar Olsen s.n., prepared from cult. (L!).

Figures

FIGURE 1. Arisaema longitubum Z.X. Ma. A. inflorescence. B. individuals in the habitat. C. female spadix. D. male spadix. Images © Zheng-Xu Ma; plants are from the population of the holotype.

FIGURE 2. Arisaema longitubum Z. X. Ma. A. mature individual, B. juvenile leaf blade, C. spathe, D. male spadix, E. synandria, F. female spadix, G. pistil. Drawn by Yi-Fan Li: A & F from paratype, B & G from isotypes, C–E from holotype.