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The Orchidaceae are one of the largest and most diverse families of flowering plants. Orchids grow as terrestrial, lithophytic, epiphytic or climbing herbs but most orchids native to the Sydney Region can be placed in one of two categories. The first consists of terrestrial, deciduous plants that live in fire-prone environments, die back seasonally to dormant underground root tubers, possess exclusively subterranean roots, which die off as the plants become dormant, and belong to the subfamily Orchidoideae. The second consists of epiphytic or lithophytic, evergreen plants that live in fire-free environments, either lack specialised storage structures or possess succulent stems or leaves that are unprotected from fire, possess aerial roots that grow over the surface of, or free of, the substrate, and which do not die off seasonally, and belong to the subfamily Epidendroideae.
Orchid seeds are numerous and tiny, lacking cotyledons and endosperm and containing minimal nutrient reserves. Although the seeds of some species can commence germination on their own, all rely on infection by mycorrhizal fungi, which may be species-specific, to grow beyond the earliest stages of development. Many epidendroid orchids are viable from an early stage without their mycorrhizal fungi but most orchidoid orchids rely, at least to some extent, on their mycorrhizal fungi throughout their lives. Some are completely parasitic on their fungi and have lost the ability to photosynthesize. Some orchids parasitize highly pathogenic mycorrhizal fungi and are thus indirectly parasitic on other plants.
Most orchids have specialised relationships with pollinating animals, with many species each pollinated by only one species of insect. Deceptive pollination systems, in which the plants provide no tangible reward to their pollinators, are common in the Orchidaceae. The most common form of deceit is food mimicry, while at least a few taxa mimic insect brood sites. At least six lineages of Australian orchids have independently evolved sexual deception. In this syndrome, a flower mimics the female of the pollinating insect species. Male insects are attracted to the flower and attempt to mate with it, and pollinate it in the process.
Little is known of most aspects of the population ecology of orchids native to the Sydney Region, especially their responses to fire. Such knowledge would be very useful in informing decisions in wildlife management.
Many aspects of the biology of Genoplesium baueri R.Br. (Orchidaceae) an endangered terrestrial orchid endemic to New South Wales, Australia, remain unknown. In this study observations were made on (1) plant morphology; (2) the biology of the fruit and seeds; (3) the biology of the plant tuber and the spatial patterning of emergent plants ; (4) the morphology of the pollen and the identity of pollen vectors and (5) to develop a preliminary description of the lifecycle of the orchid, by carrying out annual surveys of two key Genoplesium baueri populations in northern Sydney, for a 12-year period and collecting data on fruits, tubers and pollinators opportunistically. Individual plants cannot be tracked from year to year. We observed that each emergent plant produces a tubular leaf and an inflorescence of 1-15 non-resupinate flowers. Fruit capsules contained numerous tiny seeds, which were slightly larger than seeds of a closely related species, Corunastylis filiformis. The papillose surface of mature tubers of Genoplesium baueri differed greatly from the smooth, spherical tubers of Corunastylis fimbriata and is likely to be the site of orchid mycorrhizae. The occurrence of clumps of closely-packed, variously-sized tubers, each subtending single Genoplesium baueri plants, warrants investigation as development by vegetative increase at the tuber level provides one of several possible explanations. The morphology of the pollinarium and evidence of Chloropid fly-mediated pollination was observed. Our better understanding of the natural history and biology of Genoplesium baueri will contribute to orchid systematics and help inform management decisions regarding this species to ensure its persistence into the future.
Genoplesium baueri R.Br. (family Orchidaceae), an endangered terrestrial orchid species endemic to the Sydney Basin, New South Wales, Australia, is known from 13 populations but little is known about its population demographics. To assess the emergent population size, plant size and reproductive output of two key northern Sydney populations, at Ku-ring-gai Chase National Park (KCNP) and Ku-ring-gai Wildflower Garden (KWG), and how these fluctuate through time, intensive field surveys of these populations were carried out over a ten-year period (2009-18). Plants emerged at both sites in every year with a total of 1,249 plant counts made over the 10-year period. From this, we estimate that a total of approximately 500 perennial individuals may exist across both populations, more than previously thought. Although emergent population size did not differ between populations, we found significant differences between the populations in the other measures. The KWG population had taller plants that produced more flowers per plant than the KCNP population, while the plants in the KCNP population had more pollinated flowers and fruit per plant. All of these measures significantly fluctuated through time. This 10-year study has shown that the resilience of key Genoplesium baueri populations is greater than previously thought. However, it has also shown the boom-and-bust nature of emergence, flowering and fruit set in this species, which has highlighted the need for multiyear intensive studies when assessing likely persistence of endangered terrestrial orchid species.