Structural attributes of the hypogeous holoparasite Hydnora triceps Drège & Meyer (Hydnoraceae)

Abstract

The morphology of the hypogeous root holoparasite Hydnora triceps is highly reduced, and as with many holoparasites, the vegetative body is difficult to interpret. The vegetative body of H. triceps has been historically considered a "pilot root" studded with lateral appendages known as "haustorial roots." We found the vegetative body of H. triceps to consist of a rhizome with a thickened root-cap-like structure that covered a vegetative shoot apical meristem. From the apical meristem, procambial strands originated and developed into endarch collateral vascular bundles arranged radially around a pith without an interfascicular cambium. Xylem vessels had scalariform pitting and simple perforation plates. A continuous periderm without root hairs was observed. Increase in girth was attributed to cork and fascicular cambia. "Haustorial roots" or bumps on the surface of the vegetative body were exogenous, contained meristems and were the origins of vegetative branching, budding, and haustoria. The haustoria of H. triceps were cylindrical and penetrated the host root stele. Phloem and xylem elements were observed within the endophyte, and direct xylem to host-xylem contacts were observed. The arrangement of vascular tissues and xylem anatomy of H. triceps are likely plesiomorphic features in light of Hydnoraceae's placement in the Piperales.

Structure and Development of the Endophyte in the Parasitic Angiosperm Cuscuta japonica

“…4b-d) to maintain a flow of water and minerals between the parasite and its host. A lumen-to-lumen direct connection between parasite and host xylem is found in several host-parasite systems, i.e., Zea mays-Striga hermonthica (Dörr 1997), Impatiens balsaminea-Cuscuta pentagona (Vaughn 2006), and Euphorbia dregenea-Hydnora triceps (Tennakoon et al 2006). However, such direct lumen-to-lumen links between host xylem and parasite xylem were not exactly observed in this study.…”

Mineral nutrition and heterotrophy in the water conservative holoparasite Hydnora Thunb. (Hydnoraceae)

“…No chlorophyll was detected in tissues of H. africana using spectrophotometric methods (De la Harpe et al, 1981). Furthermore, H. triceps showed aggressive haustoria with direct parasite xylem-host xylem contacts and parasite parenchyma-host phloem contacts (Tennakoon et al, 2007). Their subterranean habit, lack of transpirative surfaces, stomata, and apparent holoparasitism make Hydnora a good model organism for investigating parasite-host relationships.…”

“…The vegetative body of H. triceps is a rhizome entirely covered with a suberized periderm with a chimeric growth tip that shows root and shoot characters. The highly reduced rhizome bears no stomata, leaves, or leaf scales (Tennakoon et al, 2007). No chlorophyll was detected in tissues of H. africana using spectrophotometric methods (De la Harpe et al, 1981).…”

Vegetative anatomy of <em>Lophophytum mirabile</em> subsp. <em>bolivianum</em> (Balanophoraceae) and the effect of its parasitism in the anatomy of the roots of its host <em>Anadenanthera colubrina</em> var. <em>cebil</em>

“…El cuerpo de las holoparásitas es muy variable y va desde especies en las que predomina el desarrollo exófito, como pasa en la familia Hydnoraceae C. Agardh (Meijer, 1993a;Tennakoon & al., 2007), hasta casos extremos de desarrollo del endófito, como en las familias Rafflesiaceae Dum., Mitrastemonaceae Makino, Apodanthaceae Tiegh. ex Takht.…”