Parasitic plants represent around 1.5% of all flowering species, adding up to ca. 4,750 species. The diversity of these plants, as well as aspects of their biology and evolution have drawn the attention of several naturalists and researchers — myself included! A point that is central to the discussion of how parasitic plants evolved from their non-parasitic ancestors is the development and functioning of the haustorium. This is the organ that promotes attachment, penetration and connection between parasitic plants and their hosts: “the very idea of plant parasitism.”

The prevalent interpretation is that haustoria would be modified roots since they carry out two of the same basic functions: attachment to a substrate and solute uptake.  Haustoria and roots are also similar in terms of their morphological origin, emerging either from other roots or from the root-pole of a seedling. However, this is not always the case. In some parasitic species, such as dodders (Cuscuta), haustoria originate not from the roots, but from twining stems. In this case they are generally interpreted as modified and reduced adventitious roots. The parallels between haustoria and roots seems quite straightforward until we start digging deeper.