Tropical Fern Flora of Brunei Shows Entire Fronds in Epiphytic Species and Divided Fronds in Terrestrial Species: Two Working Hypotheses to Explain Such Morphological Differences

Abstract

Fern species are famous for their frond division, often used as a fractal representation. Fronds can be entire, or divided into first, second and third orders of division. In general, fern species tend to have divided fronds, while species with entire fronds are less common. In tropical regions, where fern species reach their highest richness and morphological diversity, the frequency of entire fronds versus divided fronds has rarely been studied. In this study, I present the frond division pattern for the fern flora of Brunei Darussalam. I use the recently published checklist of the ferns of Brunei Darussalam, which lists 341 species. I also divided the species by their life form: terrestrial and epiphytic. Terrestrial species represent 60% of the Brunei fern diversity, while epiphytes represent the remaining 40%. I find that terrestrial species have the highest proportion of first-order frond division, followed by entire fronds, second-order fronds, and third-order fronds. In contrast, the epiphyte species are predominantly represented by entire fronds, followed by first-order frond division. I conclude this article with two working hypotheses to explain this remarkable morphological difference between the two tropical life forms.