﻿A new species of Typhonium (Araceae) from Vietnam

﻿Abstract Typhoniumobtusum is described as a new species endemic to Vietnam. It is unique in the genus in having an oblong-elliptic spathe limb with an obtuse apex and yellowish-greenish filiform staminodes with a down-curved acumen. The ecology, distribution and assessment of the conservation status of the new taxon, as well as a key to all known Typhonium species in Vietnam, are provided.

As part of ongoing study of Typhonium in Vietnam, we have collected several putatively new taxa, one of which was found in Phu Yen Province, central Vietnam.At the first glance, the plant looks like T. rhizomatosum A.Galloway and P.Schmidt (Galloway 2012) and T. cordifolium S.Y.Hu (Hu 1968) as all of them share the following in common: the general appearance of leaves and spathe limbs and the structure of inflorescences (Nguyen et al. 2022b;Nguyen-Phi et al. 2023).However, after our careful examination of its morphological characteristics, it turns out that our plant is, indeed, a new species that we describe here, based on living collections.

Material and methods
The studied material was collected from Phu Yen Province, Central Vietnam.Specimens were sampled and processed using methods guided by the Royal Botanic Gardens, Kew (Bridson and Forman 1999); the herbarium acronyms follow Thiers (2024).Detailed photographs and description of taxonomically important characters of the new species were taken of fresh materials in the field using a digital camera.Taxonomic identification was based on morphological vegetative and reproductive characters following the aforementioned literature.Diagnosis.Typhonium obtusum is morphologically similar to T. rhizomatosum and T. cordifolium in having ovate leaf blades with cordate base, oblong and elongate spathe limb as long as the spadix and an elongated fusiform spadix appendix.However, the novel taxon can be distinguished from T. rhizomatosum by its subcylindrical (vs.globose to subglobose) tubers without (vs.with) rhizomatous offsets, stipitate and fusiform (vs.sessile and conical) spadix appendix) and oblong-elliptic (vs.narrowly triangular ovate) spathe limb and from T. cordifolium by its subcylindrical (vs.subglobose) tubers, leaves without (vs.with) adventitious buds, oblong-elliptic (vs.narrowly triangular ovate) spathe limb and stipitate and fusiform (vs.sessile and cylindrical) spadix appendix.
Ecological notes.The new species was found growing in clumps on basalt soils in open places of rural farms.It appears in September to December and becomes dormant in January to August.Flowering and fruiting were seen in August.
Distribution.Typhonium obtusum has been recorded only from the type locality.Conservation status.Data Deficient (DD) (IUCN Standards and Petitions Subcommittee 2022).The new species has, so far, been found in one location and further inventory should be employed for a certain assessment.
Taxonomic notes.The key morphological similarities and differences of T. obtusum versus T. rhizomatosum and T. cordifolium are presented in the diagnosis.In addition, the two latter are different from the new species by their unique characters in the genus: T. cordifolium with adventitious buds appearing at the mature leaf blade apex or sometimes at the top of the sheath, while T. rhizomatosum often forms large colonies thanks to its rhizomatous offsettings (Murata et al. 2010;Boyce et al. 2012;Nguyen-Phi et al. 2023).

Figure 1 .
Figure 1.Typhonium obtusum A whole plants B stem C different forms of leaf blade D inflorescence E spathe and spadix F male, sterile and female zones G stamens H thecae, opened I pistils, cross-dissection J fruits.

Table 1 .
Morphological differences between Typhonium obtusum and close species.