Typhonium praelongum Serebryanyi & Hett., 2023

Serebryanyi, M., Trinh, T. & Hetterscheid, W., 2023, New tuberous Araceae from Binh Thuan Province (South Vietnam), Blumea 68 (1), pp. 39-48 : 40-43

Typhonium praelongum Serebryanyi & Hett. , sp. nov. — Fig. 2 , 3 , 4

Etymology. The epithet ‘ praelongum ’ refers to the extremely long sterile appendix of the spadix.

Typhonium praelongum is diagnosed by a tuber of blunt cone shape, a very long (about 30 cm) sterile appendix of the spadix with filiform upper part, rod-shaped,horizontal yellow-orange staminodes with tops turning upwards, swollen at the apex and a glossy entirely papillate upper surface of the leaf blade with impressed veins. — Type: Tan Trinh s.n. (holo MHA), South Vietnam, Nui Ong Nature Reserve , Tanh Linh District , Binh Thu ận Province, prepared from a cultivated plant originally collected in the type locality .

Seasonally dormant, small tuberous herb, flowering with leaves, up to 30(–35) cm high. Tubers of almost perfect blunt cone shape, up to 4 cm high, bottom diam 3–4 cm, top diam 1–1.5 cm, rootmassformingatthetop,offsetdevelopmentscatteredthroughout the length of the tuber ( Fig. 3f ). Petiole whitish green in basal part, changing to light-green at the top, with circular horizontal whitish stripes, the ones at the base part of the petiole sometimes dark green in mature leaves, smooth, 20–25(–30) cm long, c. 4 mm diam at the base, gradually and slightly tapering towards the apex. Leaf blade ovate to oblong-ovate, up to 20 by 12–13 cm, base deeply cordate, apex long acuminate (acumen to 2.5 cm long), margin somewhat undulate (especially the ba- sal lobes); upper surface lucid glossy green, entirely papillate, lower surface paler, also papillate, with all the veins impressed adaxially; venation reticulate, with primary lateral veins (to 12 in total; half of them in basal lobes, half in the anterior lobe) not in perfect pairs, their ends running upwards and forming an inner collective vein 0.5–0.7 cm from the margin, outer collective vein obscure and located closer than 1 mm from the margin, veins of lower orders anastomosing; midrib and posterior costa strong, especially at the base, becoming distinctly thinner towards the apex; posterior costa naked/free at least for 0.5 cm from the petiole junction (forming open sinus). Posterior lobes up to 6 by 4–5.5 cm, slightly to strongly introrse (rarely slightly overlapping). Inflorescence appearing after leaf development. Peduncle 6–7 cm long, as thick as a petiole, white. Spathe up to 17(–19) cm long, erect, completely white outside; base and limb separated by a constriction; base/lower spathe convolute, nearly globose, c. 2 by 1.5 cm diam, intensively pink inside, spathe-limb linear-oblong, open almost to the base, up to 15(–17) cm by c. 1 cm wide at the base, becoming slightly nar- rower towards the acute apex, completely white. Spadix at least twice as long as the spathe, up to 35 cm long, sessile; female zone subglobose to conical, c. 3 mm high by up to 4 mm diam at the base, 2.5–3 mm diam at the top; pistils semi-erect, up to 35 in total; sterile zone 1.3–1.4 cm long, lower 7–8 mm carrying staminodes; male zone broadly fusiform (rarely subcylindric), c. 7 by 5 mm diam at the middle, congested; appendix on a white stipe c. 5 mm long and same diameter as interstice, up to 30(–32) cm by 3 mm diam at the base, cylindric, gradually tapering to the filiform upper part (up to 5 cm from the apex), coiling while drying, pale greenish yellow, with numerous longitudinal shallow grooves throughout. Ovary elongate-ovoid, up to 1 by 0.6(–0.7) mm diam, white, one basal ovule; style absent; stigma discoid/orbicular (slightly irregular in outline), 0.3(–0.4) mm diam, c. 0.3 mm high, translucent white, surface minutely echinate. Stamens bright yellow-orange, pores apical, pollen yellow. Staminodes simple, rod-shaped, horizontally orientated with tops turning upwards, 2–4 by 0.8–1 mm diam, terete, yellow-orange; top swollen, globose, broader than the axis, colour more intense than in rest of the staminode, upper surface verruculose. Infructescence with persistent inflated saucer-shaped lower spathe. Berries ellipsoid, 4–6 by c. 2 mm diam, dirty white, crested by the old stigma remnant (brownish dot), one-seeded. Seed remarkably hard, ovoid-conical with attenuate apex, c. 3 by 2–2.5 mm diam in the thickest basal part, olive to olive-brown when mature, testa more or less smooth.

Distribution — Typhonium praelongum is so far only known from the type locality ( Fig. 1b ). Recently, the second author received photos from Da Huoai district, Lam Dong Province, probably representing another locality of T. praelongum . This remains to be confirmed.

Habitat & Ecology — Typhonium praelongum grows in dense populations, occurring within full-shade parcels between granite rocks in polydominant leafy ever green low mountain forest of complex vertical structure (2–3 strata within the tree-layer) on a steep SE slope (c. 40°); Lithocarpus spp. ( Fagaceae ) predominant in the 1st tree-stratum of 20–25 m high).

The dense populations of T. praelongum on a steep slope make a strong impression of Dioscorea -like vine.

Phenology — Flowering: end of May to beginning of June; fruiting: beginning to mid-June.

Provisional conservation status — Typhonium praelongum is so far only known from the single locality in Nui Ong Nature Reserve. Thus, we herein propose this species to be treated as ‘Endangered’ (EN B2ab(iii)) following the Red List criteria of the IUCN (2019). It is to be hoped that Nui Ong Nature Reserve will take measures to protect this species.

Note — Typhonium praelongum possesses a unique combination of diagnostic characters: tuber having a blunt cone shape, an extremely long sterile appendix with filiform upper part, rod-shaped, horizontally orientated yellow-orange staminodes with tops turning upwards, swollen at the apex and a peculiar glossy upper surface of the leaf blade with impressed veins. There are two species comparable to T. praelongum but only in a very limited number of characters, e.g., T. albispathum Bogner from Peninsular Thailand has a relatively long spathe outside pure white up to 4.5 cm long vs up to 19 cm long in T. praelongum and a long filiform sterile violet appendix up to 13.5 cm long vs up to 32 cm long pale greenish yellow appendix in T. praelongum . The most similar staminodes could be ob- served in T. ramosum Hett. (Tak province, Thailand) but these are mostly branched and are pink or orange with a dirty yellow truncate, not or only very slightly swollen top vs always simple yellow-orange staminodes with a globose swollen (capitate) top in T. praelongum . The only other species of Typhonium , having appendix of similar length (25–26 cm) is T. digitatum Hett. & Sookch. from East Thailand, but rest of inflorescence being completely different and incomparable.

Figures

Fig. 2 Typhonium praelongum Serebryanyi & Hett. in situ. a–b. Leaves; c. granite rock; d. inflorescence. — Photos by Tan Trinh.

Fig. 3 Typhonium praelongum Serebryanyi & Hett. a. Habitus (a whole flowering plant); b. leaf (upper surface); c. leaf (lower surface); d. petioles; e. seed; f. tuber; g. infructescence; h. inflorescence (bottom-up): female zone, sterile zone with staminodes, male zone, sterile appendix stipe; i. inflorescence closeup (bottom-up): female zone, staminodes. j. a whole inflorescence with spathe base cut off. — Photos by Tan Trinh.

Fig. 4 Forest community in Typhonium praelongum Serebryanyi & Hett. type locality. a. Ficus sp. reaches 1st tree stratum climbing on Lithocarpus sp.; b. canopy density; c. Cycas sp. in the 3rd tree-layer; d. fruits of Lithocarpus sp. — Photos by Tan Trinh.

Fig. 1 Tây Nguyên Plateau in Vietnam (basemap from Botov et al. 2015; used with permission).a.Tây Nguyên Plateau scheme;b. localities of Typho- nium prealongum Serebryanyi & Hett. (■) and Amorphophallus opalinus Serebryanyi & Hett. (●) (created with Simplemappr, Shorthouse 2010).