(3015) Proposal to reject the name Arum pentaphyllum (Arisaema pentaphyllum) (Araceae)

Abstract

(3015) Arum pentaphyllum L., Sp. Pl.: 964. 1 Mai 1753 (Angiosp.: Ar.), nom. utique rej. prop.

Typus: non designatus.

Linnaeus, in Species plantarum (1753: 964–967), published 22 names under Arum L., among which only one (A. maculatum L.) is currently accepted in this genus, while the other 21 names are now treated in 13 different genera (see, e.g., Jarvis, Order out of Chaos: 318–320. 2007; The Natural History Museum, Linnaean Plant Names (from The Linnaean Plant Name Typification Project) [Dataset resource], https://data.nhm.ac.uk/dataset/the-linnaean-plant-name-typification-project/resource/ec9fffe8-f7f4-4dcd-9471-641c4922d956, accessed 8 Feb 2024). One of these names, A. pentaphyllum L. (l.c.: 964–965) was described from India and appears still to be untypified.

The protologue of Arum pentaphyllum (Linnaeus, l.c.) consists of a very short diagnosis (“ARUM acaule, foliis quinatis”) and two synonyms cited from Morison (“Arum pentaphyllum indicum. Moris. hist. [Pl. Hist. Univ.] 3. p. 540 [549]. s. 13. t. 5. f. 27.” [1699]) and Zanoni (“Romphal planta indiae orientalis. Zan. hist. [Istoria Botanica] 205. fig. [LXXVIII, preceding p. 205]” [1675]); the provenance was also reported (“Habitat in India”). Both Morison (l.c. 1699: sect. 13, t. 5, fig. 27) and Zanoni (l.c. 1675: fig. LXXVIII: https://babel.hathitrust.org/cgi/pt?id=ucm.5325109245&seq=381) published almost identical illustrations, which are original material for the Linnaean name. No original specimens have been located in the Linnaean and Linnaean-linked herbaria. Therefore, the two illustrations are the only extant original material. Both match the Linnaean diagnosis in depicting a plant without stem and with leaves 5-palmate (“foliis quinatis”); both illustrations also include the spadix but no floral details are represented there.

In accordance with the treatments of Schott (in Schott & Endlicher, Melet. Bot.: 17. 1832) and Blume (Rumphia 1: 109. 1836), Jarvis (l.c.: 319) considered Arum pentaphyllum to be Arisaema pentaphyllum (L.) Schott (l.c.). Nevertheless, this name has not been otherwise accepted in any botanical publication in over a century, and in fact the illustration and Zanoni's (l.c.: 170) associated description clearly demonstrate that the name cannot be applied to any member of the tribe Arisaemateae Nakai to which the genus Arisaema belongs, because the illustrated spathe appears to be constricted with a connate tube and a gaping and erect blade, while according to Mayo & al. (Gen. Araceae: 268. 1997; in Kubitzki, Fam. Gen. Vasc. Pl.: 268–272. 1998) the spathe tube is cylindric with blade fornicate in tribe Arisaemateae.

Furthermore, there are four characters that suggest the plant cannot belong to Arisaema itself (see, e.g., Mayo & Gilbert in Kew Bull. 41: 261–278. 1989; Li & al. in Li & al., Fl. China 23: 3–79. 2010; Gusman & Gusman, Gen. Arisaema. 2006). First, the presence of an inflated spathe tube with an obvious constriction below the laminar portion does not occur in Arisaema. Second, the plant depicted in the illustration lacks a pseudostem, a structure typically present when two or more leaves occur in a species of Arisaema. Third, inflorescences in Arisaema do not usually produce a strong odour, while Zanoni (l.c.: 170) stated “e sporge un fiore stravagante […] d'odore molto acuto” (and a bizarre flower protudes […] very strong-smelling). Fourth, the plant depicted in Zanoni's illustration is strictly pentaphyllous with three larger leaflets and two smaller leaflets, a condition that does not occur in Arisaema. In Arisaema, sessile leaflets are only found in radiate leaves that have all of their leaflets emerging from a single central point at the top of the peduncle. Furthermore, although being sessile, the leaflets shown in the figure appear to be pedate in nature because their size diminishes laterally from the centre to the extremity.

The morphology of the spathe in Zanoni's illustration allows one to recognize it as a species belonging to the tribe Areae (see also Mayo & al., l.c. 1997: 253) where the spathe is usually strongly constricted, the tube with convolute margins (partially to fully connate in Sauromatum), with erect to reflexed blade and a spadix with a terminal, sterile appendix. Unfortunately the flowers, which are important for the identification of genera and species in tribe Areae (see, e.g., Li & al., l.c.), were neither depicted in the illustration nor described by Zanoni (l.c.). As such, Zanoni's illustration cannot readily be matched to any genus or species.

While the taxonomic identity of Arum pentaphyllum may be elusive if based solely on the morphology of the illustration and Zanoni's (l.c.: 170) associated description, he did provide additional information on the source of his material: “Rumphal pianta Orientale, specie d'Aro Indiano quale così vien descritta dal Padre Matteo” (Rumphal pianta orientale, a species of Indian Arum lily which has been described by Father Matteo). Matteo Ricci (Macerata, Italy, 6 October 1552–Beijing, China, 11 May 1610) was an Italian Jesuit priest and one of the founding figures of the Jesuit China missions. Before starting his missionary work in China (beginning in 1583), he was in India from 1578 (13 September) to 1582 where he lived at Goa (W-India, Goa State) and Cochin (SW-India, Kerala State) (Po-Chia Hsia, A Jesuit in the Forbidden City: 35. 2010). Both of these cities are currently included in the Western Ghats region. Zanoni evidently did not receive preserved specimens from Father Matteo Ricci, but only illustrations and descriptions of the various plants found by him in India (G. Cristofolini & U. Mossetti, pers. comm.).

Based on existing floristic accounts (e.g., Fischer in Gamble, Fl. Madras 3: 1571–1592. 1931; Sharma & al., Fl. Karnataka: 298. 1984; Sharma & al., Fl. Maharashtra: 220. 1996; Nayar & al., Fl. Pl. W. Ghats 2: 955. 2014; Sasikala & al., Fasc. Fl. India 29: 294. 2019; Mao & Dash, Fl. Pl. India Annot. Checkl. Monocot.: 172. 2020), only one species of the tribe Areae that has a leaf with five or more leaflets occurs in the Western Ghats, and that species is Sauromatum venosum (Aiton) Kunth (Enum. Pl. 3: 28. 1841), based on Arum venosum Aiton (Hort. Kew. 3: 315. 1789). The pentaphyllous leaves with three larger and two smaller leaflets (“pedate”, as described by Zanoni), absence of a pseudostem, an inflorescence producing a strong odour, presence of an inflated spathe tube with an obvious constriction below the laminar portion, and a very long yellow, undulate, and acute spathe limb with rose spots correspond to this taxon.

Since the Linnaean name Arum pentaphyllum has nomenclatural priority over A. venosum (1753 vs. 1789), the combination by Kunth (l.c.) cannot be retained and a new combination in Sauromatum based on the Linnaean basionym would be required. However, accepting A. pentaphyllum L. and its (new) combination under Sauromatum would disrupt the widely accepted usage of S. venosum, which appears in checklists and floristic works covering parts of Africa, India, and South-East Asia (Hepper in Kew Bull. 21: 492. 1967; Rao & Verma in Bull. Bot. Surv. India 18: 18. 1976; Hara & al., Enum. Fl. Pl. Nepal 1: 92. 1978; Nasir in Nasir & Ali, Fl. W. Pakistan 120: 14. 1978; Li & Hetterscheid in Li & al., Fl. China 23: 39. 2010; Nayar & al., l.c.; Sasikala & al., l.c.; Mao & Dash, l.c.) and online databases (all accessed 8 Feb 2024) such as India Flora Online (https://indiaflora-ces.iisc.ac.in/herbsheet.php?id=10942&cat=13), African Plant Database (https://africanplantdatabase.ch/en/nomen/specie/33454/sauromatum-venosum-dryand-ex-aiton-kunth), Flora of Zambia (https://www.zambiaflora.com/speciesdata/species.php?species_id=191190), Flora of Mozambique (https://www.mozambiqueflora.com/speciesdata/species.php?species_id=191190), and World Flora Online (http://www.worldfloraonline.org/taxon/wfo-0000304979). In this context the best way to avoid a disadvantageous nomenclatural change and to ensure nomenclatural stability is to reject the unused Linnaean Arum pentaphyllum, and Arisaema pentaphyllum, under Art. 56 (Turland & al. in Regnum Veg. 159. 2018).