Comparative Morphology, Anatomy, Phenology and Reproductive Biology of Alexgeorgea Spp (Restionaceae) From South-Western Western Australia

Abstract

Morphological features of Alexgeorgea nitens, A. subterranea and a recently named new species, A. ganopoda, are described. All are markedly rhizomatous and clonal, with spaced aerial culms and sand-binding roots. A. ganopoda develops nodal and internodal apogeotropic roots. Male plants bear spikelets aerially, female plants sessile underground inflorescences at a maximum intensity of one flower per season's rhizome segment. Fruiting is geocarpic and seeds are extremely large for Restionaceae, e.g. 605 mg dry weight per seed in A. ganopoda, 190 in A. nitens, 162 in A. subterranea. Germination occurs while fruits are still attached to rhizomes. Germination is hypogeal, remotive in A. nitens and A. subterranea, admotive in A. ganopoda. Graminoid seedling leaves are formed in A. nitens and A. subterranea but not in A. ganopoda. Anatomy of culm, root and rhizome conforms generally to that of other Restionaceae.

Xeromorphic features are exhibited by the two dry habitat species A. nitens and A. subterranea. Roots, rhizomes and culm bases of A. ganopoda carry interconnected cortical investments of aerenchyma, apparently as an adaptation to seasonally waterlogged habitats. Species-specific anatomical differences include the tissue architecture of culms, vascular bundle numbers in rhizome internodes and seedling leaf anatomy. Starch reserves are prominent throughout A. nitens, less so in A. subterranea and absent from A. ganopoda. Seed dry matter contains 57-59% starch. Male and female A. subterranea and male A. nitens reproduce annually. Female A. nitens flower very occasionally, mostly without setting seed. One known population of A. ganopoda is male and female fertile, the other almost entirely sterile. A. subterranea flowers in spring coincident with peak vegetative growth, A. nitens in autumn before the season's onset of growth. The reproductive phenology of A. ganopoda is unclear. The large-seededness, geocarpy and in situ germination of Alexgeorgea spp. represent an unusual form of clone replacement, resulting in establishment of seedlings within the wake of the advancing parent clone. The implications of this system are discussed.