Origin and nature of vessels in monocotyledons. 4. Araceae subfamily Philodendroideae

Tracheary elements of roots and rhizomes of five species of Araceae, subfamily Philodendroideae, representing five of the seven tribes of the subfamily, were studied by means of SEM, using macerations supplemented by sections. All except Zantedeschia albo-maculata and possibly Anthurium scherzerianum proved to have vessels in rhizomes as well as roots; only vessels in roots have been previously reported for the family. Perforation plates of rhizomes differ little from those of roots, although in some of the species pit membrane remnants are more conspicuous in rhizome perforation plates. The well-defined perforation plates of Anthurium may be related to conduction when water is available in terrestrial and epiphytic habitats that dry seasonally. Likewise, the root vessels of Zantedeschia may be related to rapid conduction during wet periods. Vessel elements of subfamily Philodendroideae represent features regarded as primitive, most notably, similarity between perforations and lateral wall pits, and the presence of pit membrane remnants in perforations. Pit membrane remnants likely are little impediment to conduction in moist tropical understory localities where most aroids grow.