Parasitism in Pholisma (Lennoaceae). I. External Morphology of Subterranean Organs

Abstract

The external features of the subterranean organs of coastal Californian Pholisma depressum Greene are described. A dimorphic root system exists. Long, stout roots (pilot roots) serve for vegetative propagation in reaching other host roots. Short, unbranching, more slender roots originating from the pilot roots are haustorial in function. Shoots seem to arise only on pilot roots. Host attachment is achieved through the direct transformation of the apical meristem of haustorial roots into the haustorial organ. The basal part of the shoot is also able to produce roots when near host roots, and may form lateral branch shoots either directly or after new haustorial connections are formed. Both types of roots arise endogenously. The invaded host root undergoes considerable hypertrophy. The intrusive organ itself forms a massive but irregular body. More than one haustorial root may enter even a small host root. Self parasitism may occur but is not common.

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

“…In contrast to the H. triceps, which has a rhizome with a root-cap-like structure, other root holoparasites have strongly dissimilar vegetative morphologies. The vegetative structure of the root holoparasite Pholisma depressum is clearly a root, based on the presence of a triarch vascular organization, lateral roots, and a thin root cap (Kuijt, 1966(Kuijt, , 1967. The unusual main vegetative bodies of Helosis cayennensis, Langsdorffia hypogaea, and Ombrophytum subterraneum are irregular spherical structures (considered tubers with few typical shoot or root characters) lacking apical meristems, roots, or leaves (Mauseth et al, 1992;Hsaio et al, 1993Hsaio et al, , 1994.…”

“…(Gedalovich-Shedletzky and Kuijt, 1990), Helosis cayennensis (Hsaio et al, 1993), Langsdorfia hypogaea (Hsaio et al, 1994), and Ombrophytum subterraneum (Mauseth et al, 1992), the host root tissue grows into the parasite tuber and the parasite forms a complex of absorptive strands. The endophyte of the root holoparasite Pholisma depressum is similar to the Hydnora endophyte in that it penetrates the host root and establishes xylem-xylem continuities (Kuijt, 1966), although no phloem was observed in the Pholisma endophyte. The Hydnora endophyte could be distinguished from the surrounding host root cortical cells by the presence of tannins in some of its parenchymatous cells and the contrasting perpendicular arrangement of host and parasite vascular tissues.…”

“…The Hydnoraceae is a root holoparasitic family and includes some of the most intriguing plants known. Without a direct requirement for sunlight, root holoparasites frequently have unusual adaptations and morphologies, quite distinct from autotrophic angiosperms (i.e., Kuijt, 1966Kuijt, , 1969Gedalovich-Shedletzky and Kuijt, 1990;Mauseth et al, 1992;Hsaio et al, 1993Hsaio et al, , 1994. The multiple origins of parasitism in the tree of life provide an example of both convergent evolution and morphological novelty in the diverse vegetative morphologies of root holoparasites.…”

Protein Profiling of Psittacanthus calyculatus during Mesquite Infection

“…In the first weeks of progression of the infection, seed adhesion, germination, seedling establishment, and organogenesis of the first true leaves occur; during the next 4–7 months the vegetative growth continues ( Figure 1 ). Thoday et al [ 57 ] described the haustorium anatomy and penetration of many Santalales species, however, they only described the phenomena for seven of the twelve currently recognized parasitic plant lineages [ 58 , 59 ]. Hence, there are no data about the chronology of development and penetration of haustoria in P. calyculatus .…”