Arisaema sceptrum Z.X.Ma, 2025

Ma, Zhengxu, 2025, Materia Revisionis Arisaemarum: III. taxonomic notes and five new taxa of the genus Arisaema (Araceae) from South China, Phytotaxa 697 (1), pp. 47-67 : 54-57

3.2. Arisaema sceptrum Z.X.Ma , sp. nov. ( Figs. 6 , 7 )

Arisaema sceptrum is similar to A. clavatum and A. silvestrii , but differs in having a tall, caulescent pseudostem, to 1.2 m long, a pedate leaf blade with 11–17 leaflets, a strongly bicolorous spathe, dull dull green abaxially and dark purple adaxially, a claviform appendix, not abruptly capitate nor exerted from spathe, apex with dark purple, raised, anastomosed venations. This species is also similar to A. heterocephalum subsp. okinawaense H.Ohashi & J. Murata (1980: 293) , but differs in having more leaflets, 11–17, an uncapitate spadix-appendix, with dark purple anastomosed venations at apex, and an endemic distribution to the Karst regions in S Guizhou, mainland Asia.

Type: — CHINA. Guizhou Province: Libo County, along road Y006, Maolan, Shishangsenlin, in limestone crevices, 21 March 2024, Y.E.Wang 334 (holotype BAZI!, isotypes BAZI!, E!, PE!).

Perennial geophyte, to 1.2 m tall, seasonally dormant, paradioecious. Subterranean stem tuberous, creamy white, erect to slightly deflective, subglobose to depressed globose, to ca. 7 cm in diam., rarely bearing tubercles; axillary bud scale-like and 4–6 in a group. Eophyll unknown. Cataphylls ca. 3, membranous, free. Foliage leaves 2; petiole glossily dark green, mottled with purple and brown, cylindric, to 1 m long, the proximal ½ part sheathing into pseudostem, petiolar sheath free; leaf blade pedate; leaflets 11–17, pale green, thick membranous, entire, oblong or oblanceolate, base cuneate, subsessile to shortly petiolulate, apex long-acuminate and attenuate; laminae venation brochidodromous, forming a smooth collective vein near leaf edge; central leaflet 16.5–32.6 × 3.3–9.7 cm, usually the largest or sometimes slightly shorter than the adjacent leaflets, shortly petiolulate at base; outermost leaflet 1.5–8.5 × 0.5–2.7 cm, sometimes minute; rachis 13.5–28.4 cm long. Inflorescence solitary, always borne on the pseudostem, positioned below leaves when female, above when male. Spathe tube abaxially green and thickly glaucous, adaxially glossily pale green with thick longitudinal purple striation, fading distally, cylindrical to narrowly funnelform, 6.9–9.8 cm long, 1.1–1.9 cm in diam.; spathe mouth purple, rounded; spathe limb dull green abaxially, dark purple adaxially, broad lanceolate, 6.5–12.9 × 2.9–5.4 cm, acuminate to the apex. Spadix dioecious, 6.9–12.4 cm long; female zone short subpyramidal, 2.5–2.7 cm long; gynoecium densely arranged; ovary greenish, obovoid; ovules 3–4; placentation basal; style obscure; stigma subglobose, whitish pubescent; male zone subpyramidal, 1.9–2.4 cm long; androecium lax; synandrium consisting of 2 bithecal anthers, cofiliment short; thecae pale purple, globose, dehiscing by a short slit resulting in an apical pore; appendix whitish, often molted with purple, claviform, swollen, 5.4–9.7 cm long, 0.5–0.9 cm in diam, base attenuate and loosely covering curved and subulate neuters, apex obtuse, with dark purple, raised, anastomosed venations. Infructescence and seeds unknown. Anthesis from February to March.

Distribution: —Karst region in S Guizhou, possibly in N Guangxi.

Eponymy: The epithet “sceptrum ”, a latinized form of the Greek word “σκῆπτρον”, refers to a rod or staff, a symbol of sovereign authority, which is often highly ornamented, and here it is metaphorically used to describe the spadix-appendix, featuring the complex dark purple anastomosed venations on the apex.

Additional specimens examined (paratypes): — CHINA. Guizhou Province: Libo County, along road Y006, Maolan, Shishangsenlin , in limestone crevices, 19 March 2024, Y.E.Wang 300 (BAZI!, PE!) ; loc. ibid., along road Y002, Daodonghua , in limestone crevices of ravine forest understory, 22 March 2024, Y.E.Wang 348 (BAZI!, PE!) .

Notes: — Arisaema sect. Clavata is a coherent group, distinguished by a unique combination of characteristics: (1) quincuncial phyllotaxy, (2) multiple accessory buds accompanying auxiliary bud on the subterranean stem, (3) pedate leaf blades, and (4) a sessile, claviform to flagellate spadix-appendix with short, acute neuters present at the base ( Li et al. 2010 p. 49; Murata 2011 p. 26, Ohi-Toma et al. 2016).

Recently, three new species from this section were described in China: A. hui (in this publication), A. jiufushanense Ma & Chen (2024: 287) , and A. sceptrum (in this publication). Based on my personal observations of the species of this section, I have noted remarkable morphological consistency, especially in the number of leaflets, pseudostem height, and spathe characters (e.g. shape and coloration of the tube and mouth). The form of the spadix-appendix is also diagnostic at the species level. Among the species with a cylindrical spadix-appendix, A. clavatum shows a diverse pattern of morphological variation in its spadix-appendix, yet its apical ornamentation—consistently capitate and ranging from rugose to echinate—remains relatively stable. Nonetheless, for a more comprehensive understanding of this group, future cladistic and cytogeographic studies on population level are required.

The geographic distribution of A. sect. Clavata is also noteworthy. Endemic to the subtropical Sino-Japanese flora, this section includes nine species that display a disjunct distribution extending from continental East Asia to the southern Japanese Archipelago ( Murata 2011 pp. 62, 70). Of these, six species are restricted to continental East Asia: A. hui , A. clavatum , A. hunanense , A. jiufushanense , A. sceptrum , and A. silvestrii . The remaining species are found on Pacific islands, with A. ilanense Wang (1996: 71) on Taiwan Island, A. heterocephalum Koidzumi (1928: 12) in the Ryukyu Islands ( Murata 1985), and A. negishii Makino (1918: 41) in the Izu Islands.

The disproportionate concentration of species (⅔) in continental East Asia, particularly in the Wuling Mountains and its north-south extensions through southwestern Hubei, southeastern Chongqing, eastern Guizhou, western Hunan, and northern Guangxi, suggests that this region is the center of distribution (and even center of origin) for A. sect. Clavata , though currently still poorly understood and having been overlooked by the previous studies.

4. Arisaema sect. Flagellarisaema ( Nakai 1950: 6) H. Hara (1971: 326) . Type:— Arisaema thunbergii Blume (1836: 105)

4.1. Arisaema autumnale (J.C.Wang, J.Murata & H.Ohashi) Z.X.Ma , stat. nov. Basionym:— Arisaema thunbergii Blume subsp. autumnale J.C.Wang, J.Murata & H.Ohashi in Wang (1996: 75). Type:— CHINA. Taiwan: Taipei Hsien, Sanhsia, Hsiung-kung to Man-yue-yuan, on the floor of broadleaf forest, Wang, Sang & Chen 9460 (holotype TNU!, isotypes HAST!, TNU!)

Notes: — Arisaema autumnale , endemic to the Taiwan Island, is found in the central montane region of the island. In his systematic treatment of Taiwanese Arisaema species, Wang (1996) initially classified A. autumnale as a subspecies of A. thunbergii , and identified a few distinct morphological differences between it and A. thunbergii subsp. urashima . Notably, the spathe of A. autumnale is diagnostic of a less expanded limb and prominent longitudinal striations on both surfaces ( Wang 1996, Omori et al. 2004). Furthermore, the flowering season of A. autumnale is highly differentiated, occurring exclusively in the autumn months of October to November, in stark contrast to the springtime bloom of all other subspecies of A. thunbergii (April to May, as reported in Murata 2011 p. 100). Wang (1996) attributed this unique phenology to an adaptation to a warm subtropical climate of A. autumnale ’s habitat.

More recently, molecular phylogenetic evidence presented by Ohi-Toma et al. (2016) and Tran et al. (2022) has challenged our understanding of the taxonomic relationships within A. thunbergii s.l. by revealing the paraphyletic nature of A. thunbergii . This also challenged our understanding of the pattern of morphological variation in this species, especially emphasizing the special role that anthesis differentiation may play in speciation. Consequently, given the combined evidence, it is reasonable to propose upgrading A. autumnale to species status.

4.2. Arisaema brevistipitatum Merrill (1934: 19) . Type:— CHINA. Kwangtung [Guangdong]: Tseng-shing District [Zengcheng Qu], Naam Kwan Shan [Mt. Nankun Shan], Apr. 7, 1932, in a dry bamboo garden, W.T.Tsang 20149 (holotype NY [barcode: NY 00133839]!, isotypes 1 A [barcode: A00025760]!, PE [barcode: PE 00032460]!, SYS [barcodes: SYS 00022361, SYS00022362, SYS 00095397]!, US [barcode: US 00088066]!). = Arisaema melanostomum Z.X.Ma, X.Yun Wang & W.Y.Du (2019: 266) , syn. nov. Type:— CHINA. Guangdong Province: Shenzhen City, Yantian District, Yantian Sub-district, Sanzhoutian, ca. 450 m, 14 April 2018, Z.X.Ma 0021 (holotype: PE [barcode: PE 02333685]!, isotypes HK, PE [barcode: PE 02333689]!)

Notes: —It has come to my attention that A. brevistipitatum is an earlier name that was inadvertently overlooked. Upon the publication of A. melanostomum , a thorough examination of the type of A. brevistipitatum was not conducted, resulting in a misunderstanding that they represented distinct entities. However, upon further review of the holotype, it is evident that both names refer to the same species. Therefore, I hereby merge the later-published A. melanostomum with A. brevistipitatum to reflect this understanding.

Figures

FIGURE 6. Habit of Arisaema sceptrum. A. Female individual; B. male individual.All photos are vouched by Y.E.Wang 348 (BAZI!).

FIGURE 7. Inflorescence of Arisaema sceptrum. A. Inflorescences showing range of variation; B, C. inflorescence in different views; D. adaxial spathe surface with a dark purple coloration; E. female spadix; F. male spadix; G. apex of spadix-appendix, note the finely raised dark purple reticulate venation. All photos are vouched by Y.E.Wang 348 (BAZI!).