Tetrastigma leucostaphylum (Dennst.) Alston ex Mabb. Partial Wedge Sampling, a New, Less-invasive Solution for Stem-borne versus Root-borne Rafflesia Identification

Abstract

Tetrastigma (Vitaceae) are a genus of tropical lianas that are hosts for parasitic plants in the family Rafflesiaceae. Since the stem of Tetrastigma is creeping and often devoid of leaves, it is often mistakenly visually identified as a root. Rafflesia flowers at the ground level (i.e. terrestrial flowers) have been documented to grow on Tetrastigma roots, but it is unclear whether those that arise aerially emerge from host root or stem organs. In this study, we present a new, lessdestructive means of sampling Tetrastigma leucostaphylum, which is a host of many Rafflesia species. Histological observation of two 250 cm above-ground aerial samples confirmed that both were stems, as shown by distinct anatomical features (compactly arranged vascular bundles with simple phloem bundles) in contrast to roots, which had loosely arranged vascular bundles with ramified phloem bundles. Clearer identification of Tetrastigma vine infected with aerial Rafflesia is needed to confirm whether the parasitic flower grows on a stem or on an erect aerial root to better understand the biology of this enigmatic Rafflesia species that have evaded cultivation and ex situ conservation efforts. This new sampling method may be a useful way to identify the Tetrastigma vine in the future due to its less invasive nature compared to severing the whole vine.