Borneo and its disproportionately large rheophytic aroid flora

Abstract

On the basis of decades of field observations and multidisciplinary research, in particular directed at species of Araceae exhibiting rheophytism, we offer an overview of morphological diversity among the more than 130 aroid species so adapted on Borneo. Based on a combination of morphological and concomitant ecological occurrence, a preliminary scheme of subcategories of van Steenis' "rheophytic landplants" is outlined with the purpose of encouraging study to better understand the impetus of obligate rheophytic aroids' evolution. It is hoped that the proposed subcategories will encourage targeted research with abundant field-based observations. Criticism is directed at the current demand by scientific journals that computer algorithm-generated statistical 'proof' be provided for all observational life science writing and further insisting that all such observations be linked to a 'big picture' by comparison within the context of a global perspective, preferably incorporating whatever themes are currently fashionable in the field. Such requirements discourage researchers, and particularly students, from undertaking purely observational research, and effectively result in the suppression of publication of vital observational data while encouraging publication of statistically well-supported biological nonsense.

A synopsis of the endemic plant genera of Borneo

“…On the other hand, endemic genera which might be the products of recent evolution but not yet expanded in geographic distribution could include those of the Schismatoglottideae tribe of predominantly rheophytic Araceae. The rheophytic aroids are known to be obligated to diverse geologies (Boyce and Wong ), suggesting adaptive radiation. Moreover, they are limited in dispersal, their seeds typically dispersed from a splash cup (rain splash is known to carry seeds to a maximum distance of 1 m; Amador et al ) or carried away by flowing water in their typically riparian habitats.…”

Distribution of Araceae and the Diversity of Life Forms

“…Very little of its overall surface has been explored and a thorough study of the region could potentially produce numbers of species that would dwarf existing number of known species. Similar studies in some parts of Asia may be equally rewarding, particularly in Southeastern Asia, in Borneo, where evolution has taken a path dictated by edaphic differences in soil type among a largely riparian group of Aroids, mainly in Homalomeneae and Colocasoideae and possibly also in Schismatoglottideae (Boyce & Wong, 2019). The high potential for novel species is reflected in a list published online (Boyce & Croat, 2011) which attempts to reflect the present status of all aroid genera in the world, listing the number of published species and the number of anticipated unpublished species.…”

“…The two former genera are Asian, terrestrial, and largely occur in the forest understory and as riparian herbs along streams. Homalomena has evolved extensively in Borneo with many species adapted to different edaphic conditions (Boyce & Wong, 2019). Adelonema, in the neotropics consists of understory herbs largely in moist to wet forest (Wong et al, 2013).…”

“…The rheophytes clade (sensu Cusimano et al, 2011), which includes a high representation of rheophytes (Boyce & Wong, 2019) and aquatics, comprises two main subclades: Cryptocoryneae and Schismatoglottideae. The Asian tribe Schismatoglottideae has a growth habit similar to Homalomena with many species evolving in edaphically unique habitats, mostly aquatic or riparian habitats, but also as understory herbs that are not directly associated with streams.…”

Hanguana deflexa (Hanguanaceae), a new forest species from Sarawak, Borneo

“…While the diversity of some families is well to moderately well explored (e.g. Araceae and Zingiberaceae ; Smith 1985 , 1986 , 1987 , 1988 , 1989 ; Boyce and Julia 2006 ; Boyce and Wong 2015 , 2019 , and to some extent also Lowiaceae and Taccaceae ; Poulsen and Leong-Škorničková 2017 ; Syauqina et al 2019 ; Wong and Chua 2019 ; Leong-Škorničková et al 2021 ), the diversity of others remains poorly understood (e.g. Hypoxidaceae , Hanguanaceae ).…”