DID YOU KNOW? The remarkable rare Western Australian underground orchid, Rhizanthella gardneri, that spends its entire life cycle hidden from view in the dry and parched soils of the interior. Probably no more than 50 plants left in nature. Photo: Rhizanthella gardneri, Western Australia (Courtesy Kingsley Dixon & Australian Government, Dept. of Environment) Description The Underground Orchid is a succulent, subterranean orchid (Brown et al. 1998; Rye et al. 1982). The species is dependant on a mycohrrizal symbiosis (fungal relationship), and occurs within Broom Bush (Melaleuca uncinata) shrubland (Mursidawati 2004). Flowering of the Underground Orchid begins in late May to early June when each plant produces up to 100 small, inward facing, cream to reddish coloured flowers, surrounded by 6–12 large, cream or pinkish-cream bracts (Brown et al. 2003). These bracts form a tulip-like head that curves over the flowers forming a small opening at the soil surface (Brown et al. 2003). A layer of leaf and bark litter covers this opening (Brown et al. 2003). The plants have a horizontal rhizome 6–12 cm below the ground level, which, like the rest of the plant, is succulent and produces a formalin-like odour when cut (Brown et al. 2003). Once pollinated, each flower produces a berry-like indehiscent fleshy fruit containing 20–150 seeds (Brown et al. 2003). This type of fruit is unique amongst the Western Australian orchids as species in all other orchid genera produce a dehiscing pod from which thousands of minute seeds are dispersed by the wind (Brown et al. 2003). Population Information The Underground Orchid is estimated to have less than 50 plants in total (Brown et al. 2003), although this may be an underestimate since flowering plants are hard to detect and the ratio between flowering and non-flowering plants is unknown (Brundrett 2011). Intensive surveys at known sites in 2001–02 found 27 plants in total (Brown et al. 2003). Life Cycle Reproduction The Underground Orchid flowers between May and July. The flowers are self compatible but do not appear to autofertilize. The main pollinating agent is unknown, but tiny wasps, gnats, ants and termites have occasionally been seen visiting the plants (Brown et al. 1998; Carstairs & Coates 1994). It is possible that the succulent fruit is eaten by small marsupials and the seeds passed out in their faeces (Hoffman & Brown 1998). Seeds mature in November and December but seed set appears to be low (Rye et al. 1982). Rhizomes of the Underground Orchid are capable of vegetative division, so it is likely that plants located with a few metres are the same individual or closely related (Brundrett 2011). Consequently, a population genetics study is required to determine the size of individuals of this species and the number present at each location (Brundrett 2011). Mycorrhizae The mycorrhizal fungus utilised by the Underground Orchid has been morphologically identified as Thanatephorus gardneri, although further investigations suggest that the fungus is from the Ceratobasidium genus (Bougoure et al. 2009). Reliance on the mycorrhizal fungus, and the association with Broom Bush, may help clarify the distribution of the Underground Orchid (Bougoure et al. 2010). Fire ecology The fire requirements of the Underground Orchid are not well known, but the species may react positively to some level of disturbance due to the increased nutrient availability, reduced competition with surrounding vegetation and smoke induced triggers (Bougoure et al. 2008).
Posted on: Sat, 13 Dec 2014 18:46:51 +0000
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