Abstract
- Holzapfel, S.: Studies on the New Zealand root-parasite Dactylanthus taylorii (Balanophoraceae). – Englera 22: 7-176. 2001.
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Dactylanthus taylorii (Balanophoraceae) is a root-holoparasitic flowering plant endemic to New Zealand. The development and anatomy of its female flower and derivates, germination, vegetative reproduction, the morphology and function of infectious roots, and the genetic diversity of populations are investigated. Other notes include history of research on the species, its general habit, systematic position, distribution, human use, and a brief description of the male flower. The female flower is comprised largely of a single ovary, and is characterised by a central pistil-like structure in which two embryo sacs develop. Various interpretations of this structure in the literature are discussed, and it is concluded that it is homologous to one or several nucelli, and may include also non-nucellate tissue. In the absence of integuments an orthodox terminology of ovule type is not regarded as useful. It is argued that the frequently cited development of the ‘micropylar’ megaspore into an embryo sac in Balanophoraceae is based on a misinterpretation of the orientation of the ovarian structures, and that all taxa studied so far follow in their development the common Allium or Polygonum type. The development of the endosperm and the morphology of the embryo in D. taylorii are investigated for the first time. Germination of the fruits and their attachment to a host root are described in detail, and results of three, only partially successful germination experiments are given. Seeds of D. taylorii are able to germinate in the absence of any host, and germinated seeds survive for a prolonged period of time in the soil. Vegetative reproduction through specialised infectious roots formed at the base of inflorescences is confirmed. Infectious roots and radicles are identical in morphology, and are characterised by hair cells with micro-papillate, bulbous bases. The ultrastructure of the micro-papillae is examined, and their possible function discussed. Both radicles and infectious roots show a tropic reaction to the presence of a possible host, but this reaction is not limited to host roots alone and is seen as rather unspecific. A hypothesis is put forward for the germination strategy in D. taylorii. The use of random amplified polymorphic DNA (RAPD) for the investigation of genetic diversity in the endangered D. taylorii is evaluated, and the suitability of the technique confirmed. Preliminary results using samples from three populations show a distinctness even of neighbouring populations. The occurrence of monoecy is not supported by genetic analysis, rather, tubers that bear inflorescences of different sex are seen as consisting of several individuals growing closely together (chimaeras). Implications of these findings for the conservation of species are discussed.