Root hemiparasitism in Malania oleifera (Olacaceae), a neglected aspect in research of the highly valued tree species.

ABSTRACT

Malania oleifera (Olacaceae) is a valued tree species, mostly because its seeds have high precious fatty acid content (particularly nervonic acid). However, seedling mortality rates are often high and regeneration of this tree has been problematic, which greatly hinders its utilization at a large scale. Cultivation difficulties of some tree species in the family Olacaceae have been attributed to their root hemiparasitic habit. Prompted by field observations and the taxonomic proximity of M. oleifera to root hemiparasites in Olacaceae, we hypothesized that tuberous structures observed on the roots of M. oleifera are parasitic organs known as haustoria. To test this hypothesis, we collected root samples from M. oleifera plants of various ages and growth conditions, investigated the morphological and anatomical features of tuberous structures and their connections to neighboring roots. Our analyses confirmed that M. oleifera are root hemiparasites. To the best of our knowledge, this is the first empirical report on root hemiparasitism in M. oleifera. Because life strategies of root hemiparasitic plants differ greatly from autotrophic plants, the root hemiparasitic habit needs to be taken into account for successful seedling regeneration of M. oleifera. This study establishes the foundation for investigations into a long-neglected but essential aspect in research of these highly valued tree species.