Pothos grandis

(Araceae: Pothoideae)

described and validated and architectural notes on Pothos subgenus Pothos

Peter C. Boyce * & Nguyen Van Dzu**

Summary. Pothos grandis, a name proposed but not validly published by Buchet (1942), is validated and an emended species description given. Discussion of the growth architecture of western Indomalesian Pothos subgenus Pothos is presented.

Pothos L. is genus of approximately 70 species of subtropical and tropical forest climbers centred in Malesia (Hay et al. in press) belonging to Araceae subfamily Pothoideae (sensu Bogner & Nicolson 1991). Shared leaf, flower and fruit characters suggest that Pothos is most closely related to Pedicellarum M. Hotta (1976) and Pothoidium Schott (1857a, b). Indeed, Pothos and Pedicellarum may be congeneric. Until a full revision of Pothos is completed we are, in this and other papers, adopting a modified, informal version of Engler’s infrageneric classification of Pothos (Engler 1905). While we follow Engler’s sections (as subgenera) we reject his serial concepts, instead recognizing informal species groups. Pothos grandis belongs to the P. seemanii Schott group of subgenus Pothos.

HISTORY OF Pothos grandis
Buchet (1942) writing in Gagnepain’s Floré Général de l’Indo-Chine proposed the name Pothos grandis for specimens collected at three sites in Tonkin (modern North Vietnam) and a single specimen from Annam (central Vietnam). Unfortunately, Buchet omitted the Latin diagnoses for his new species and thus according to the Art. 36.1 of the International Code of Botanical
NCNST, Nghia Do, Tu Liem, Hanoi, Vietnam.
NOMENCLATURE (Greuter et al. 1994) the name Pothos grandis is not validly published. Since Buchet’s time the species has been seldom re-collected. All collections seen are rather poor and none display the full range of shoot form to be expected for a species of Pothos subgenus Pothos. Recent field work in North Vietnam undertaken jointly by staff of the Herbarium, Royal Botanic Gardens, Kew, (K), the Department of Botany of the Institute of Ecology and Biological Resources, Hanoi (HN) and the Department of Botany, University of Hanoi, (HNU) resulted in the re-collection of P. grandis at one of the type localities. A plant was found in flower and sufficient material collected to enable a complete description to be prepared.

Pothos grandis S. Buchet ex P.C. Boyce & D.V. Nguyen sp. nov., P. grandis in aspectu P. seemanni valde proxima, et ab ea foliis majoribus, pedunculo petiolum aequanti sed numquam eum superanti (pedunculus in P. seemanni petiolo duplo longior), spatha aliquantum grandi atque spadice dissimiliter formato grandiore in stipite longiore suffulto distinguibilis. Typus: Colani s.n. (holotypus P!; isotypi K (photo!) SGN!).

Pothos grandis S. Buchet apud Gagnepain in Lecomte, Fl. Gén. l’Indo-Chine 6: 1088 (1942), nom. invalid. sine descr. Latin.
Moderately robust somewhat woody root-climber and hammock-forming hemi-epiphyte to 3 m.

Shoot system differentiated into several phases (seedling phase not known). Seedling/mature sterile transition shoots monopodial, apparently of indeterminate length, climbing, appressed to substrate and rooting moderately from most nodes, probably not branching unless damaged apically (reiteration not observed), stem to 4 mm diam., sharply four-angled, minutely winged along the angles, leaves rather scattered. Mature sterile shoots monopodial, orthotropic, of indeterminate length, climbing, appressed to substrate and rooting prolifically from each node, not branching unless damaged apically, reiteration occurring from a node some distance back from the damaged apex, stems occasionally transforming terminally into a foraging flagellum (see below), stem to 8 mm diam., weakly four-angled or slightly compressed-terete, at first somewhat sparsely clothed with leaves, later naked, naked portions with prominent, slightly stepped nodes to 5 cm distant, stem deep green, becoming black-brown with age, drying dark green to almost black. Mature fertile shoot sympodial, with growth modules of varying determinate lengths, free, arising from the mature sterile stem as side branches, often branching to three orders, plagiotropic, not rooting from nodes, stem to 4 mm diam., mostly moderately clothed with leaves, occasionally older portions naked at the base to approximately half their length, naked portions with prominent, stepped nodes to 3 cm distant. Flowering shoots much abbreviated, arising from the leaf axils of mature fertile shoots, subtended by a minute prophyll and up to seven 4 - 30 mm, sequentially longer, cataphylls, terminated by 1 - 3 sequentially-produced inflorescences. Foraging shoot a flagellum to 2 mm diam. with a few leaf-like cataphylls and reduced foliage-leaves at first but soon becoming naked with slightly prominent nodes up to 10 cm distant, arising mostly by terminal extension of the mature sterile shoot, (more rarely from a similar extension of a fertile shoot), monopodial, of indeterminate length, foraging for several metres until a suitable climbing surface is encountered, not branching unless damaged apically and then branching from the nearest healthy node, occasionally rooting sparsely from the nodes while foraging, always rooting prolifically on resumption of climbing habit.

Leaves: Petiole obovate-oblong, broadly winged, base decurrent, apex truncate to rounded or slightly auriculate, 2 - 5 x 1 - 2 cm, petiole with 2 - 3 secondary veins and numerous veinlets per side, all veins prominent, especially in dried material; lamina ovate, base rounded, apex acuminate-mucronate, 14 - 23 x 5.5 - 10 cm, lamina with 2 secondary veins per side, these arising from the base and either reaching the leaf tip or merging into a prominent submarginal collecting vein, all additional veins arising obliquely from the mid-vein, remaining parallel with numerous branches arising from them, leaves deep green adaxially, paler and slightly yellowish abaxially when fresh, drying dull olive green.

Inflorescence pedunculate, peduncle robust, 4 - 7 cm x 2 - 3 mm, tapering, slightly thinner towards the apex, deep purple; spathe ovate to ovate-lanceolate, base slightly cordate to decurrent, apex acute with a somewhat stout mucro, 2.5 - 5.2 x 2 - 3 cm, margins prominently inrolled, deep purple, sometimes slightly greenish abaxially when fresh, drying almost black; spadix stipitate, deep purple, stipe terete, 1.2 - 1.5 cm x c. 2 mm; fertile portion of spadix ovoid to clavate, 1.2 - 3 cm x 9 - 13 mm, yellow-green to off-white.

Flowers: tepals 6, 4 x 1.3 mm, oblong-cymbiform, yellow-green to dirty white, apex cucullate, triangular, truncate, stamens 6, 1 - 4 x c. 0.5 mm, filaments strap-shaped, thecae elongate-globose, 1 x 0.25 mm, dehiscing via longitudinal slits, cream, gynoecium 5 x 1.75 mm, 3-locular, compressed angular-ellipsoid, yellow-green to dirty white, stylar region truncate, stigma prominent, punctate, purple.

Infructescence a head of 4 - 10 berries, these obclavate, 1 - 1.75 x 1 - 1.4 cm, green ripening through yellow to deep orange-red. Seeds 1 - 3, ellipsoid to compressed-globose, c. 5 - 8 mm diam. (Fig. 1).
VIETNAM. Hanoi: near Kien Khe, Bon 2152 (P!). Ha Tay: My Duc, Chua Huong, 28 May 1977, Nguyen Thi Nhan HN 111 (HN!); My Duc, Chua Huong, 1 July 1993, Ha Thi Dung HN 217 (HN!); Hoa Binh: Cho Bo, Balansa 2051 (P!); Kim Boi, 30 Aug. 1994, Boyce & Nguyen Van Dzu 857 (HN!, K!); Kim Boi, June 1926, Colani 3002 (holotype P!; isotypes K (photo), P!, SGN!); Kon Tum, Dak Glay, 29 Mar. 1977, Tran Ding Ly HN 389 (HN!); Lang Son: Pac Mo, 23 Mar. 1961, Soviet-Vietnam Expedition 1137 (LE!); Nghe An: from Phu Qui to Kebon, Poilane 16565 (P!, SGN!); Quy Chau, Trinh Xuan Mai HN 737 (HN!). Ninh Binh: Cuc Phuong Nat. Park, 6 Jan. 1963, Nguyen Quo Chung HN 2130 (HN!); Cuc Phuong Nat. Park, 17 Feb. 1971, Hach 26 CP (HN!); Cuc Phuong Nat. Park, 9 July 1971, Tran Hop HN 643 (HN!).

ECOLOGY. Climber or hemiepiphyte on trees and cliffs of Karst limestone formations in fragments of very degraded lowland to lower hill evergreen forest. 75 - 250 m.

VERNACULAR NAME: Co´m lênh la´buo´i (Viet.).
NOTE: The collection from Pac Mo, Lang Son prov., (Soviet-Vietnam Expedition 1137) was made close to the border with China. Pothos grandis is to be expected in that country.
Pothos grandis is most similar in appearance to P. seemanni Schott (SW China, Laos, Thailand, N Vietnam) from which it may be separated by the larger leaves, the peduncle equalling the petiole (peduncle twice as long as the petiole in P. seemanni), larger, differently shaped spathe (ovate to ovate-lanceolate in P. grandis, ovoid in P. seemanni), the differently shaped, larger fertile portion of spadix (ovoid to clavate in P. grandis, ovoid in P. seemanni) and longer stipe.

Pothos grandis displays the typical growth architecture and inflorescence presentation of most species of subgenus Pothos and can be used as a point of reference for a discussion of the majority of species of this subgenus in western Indomalesia. Species of the Pothos scandens L. group (subgenus Pothos), while conforming to the pattern of growth architecture described above, behave somewhat differently in the manner of inflorescence presentation. Discussion of this will be the subject of a future paper. Data concerning stem architecture in P. insignis Engl. (Borneo; subgenus AlloPothos) were discussed by Boyce and Poulsen (1994, as sect. AlloPothos).
Most species of subgenus Pothos in western Indomalesia appear to have the five-phase growth architecture described above for P. grandis (Fig. 2). A possible sixth phase, a modified version of the sterile mature growth, has been observed in three species of Pothos and is discussed below. The seedling stage is not known for all species in the subgenus but for those known, P. scandens L., P. repens (Lour.) Druce (syn. P. loureirii Hooker & Arn.), P. longipes Schott (see Hay, in press), P. cathcartii Schott and P. yunnanensis Engl., this phase consists of a skototropic (see Strong & Ray 1975) flagellar growth which, on reaching a suitable climbing surface, alters into a shingle climber with closely arranged or overlapping leaves of much the same shape as those found in the adult growth stages. The shingle stage appears to be monopodial but also produces simple branching systems by reiteration (sensu Hallé, Oldemann and Tomlinson 1978). The seedling phase continues until one or more as yet unknown factors (e.g. light and moisture levels, available nutrients) trigger the production of the sterile mature growth stage. This stage is a densely leafy, later naked, appressed monopodial climber rooting copiously from the nodes. The sterile mature growth phase does not branch terminally unless damaged when it then reiterates from a node usually some distance back from the damaged apex. However, this phase does occasionally transform terminally into a foraging flagellum as discussed above for P. grandis. At some point the sterile mature stage begins to produce fertile mature shoots from lateral buds. These fertile shoots are sympodial, of varying determinate lengths and often branch to several orders from lateral buds. They are generally moderately leafy, later becoming naked below. Fertile mature shoots eventually produce much-abbreviated lateral shoots consisting of a minute prophyll and one to several cataphylls and terminating in one to several sequentially-produced inflorescences. Occasionally fertile mature shoots transform terminally into a foraging flagellum.
In P. scandens (observed in cultivation at Kew), P. macrocephalus Scort. ex Hook.f. (observed in cultivation at Leiden), P. repens and P. cathcartii (both observed in habitat), the sterile mature growth phase occasionally produces exceptionally robust lateral branches in which the leaves, while of conventional shape and size, are tightly imbricated and not spreading. The factors triggering this modified growth phase are not known. It might represent another form of foraging shoot or, possibly, a means for the plant to reiterate from lower buds when the top growth carried begins to exceed the capability of the functional root mass. It is noteworthy that this type of sterile mature shoot reiteration has only been observed on plants of great size, most notably an immense specimen of P. repens covering almost an entire Karst limestone formation at Man Duc, Hoa Binn province, Vietnam.

We would like to thank Dr David Simpson and Dr Alistair Hay for their comments and suggestions and Mr Alan R. Radcliffe-Smith for the Latin translation of the diagnoses.

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* Herbarium, Royal Botanic Gardens Kew, Richmond, Surrey, TW9 3AB, U.K.

** Herbarium, Department of Botany, Institute of Ecology & Biological Resources,