Crotalaria cunninghamii

Crotalaria cunninghamii was identified By Alan Cunningham on a naval expedition in North Western Western Australia in the 1810s. During a seven-month trip to North Western Western Australian in 1817, Cunningham collected more than 300 different species, one of which was Crotalaria cunninghamii. Alan Cunningham landed on the shores of Parramatta in 1816 and swiftly started exploring and identifying plant species in Australia. After recovering from a severe fever suffered during an expedition west of the Blue mountains in 1817, Cunningham was asked to join a naval expedition to North West Western Australia which he gladly accepted. Cunningham made two more naval expeditions over the following years. His third voyage was almost disrupted due to a serious leak. Their ship, the cutter Mermaid, was then promptly fixed in Careening Bay, and Cunningham was free to discover hundreds more plants in Australia before returning to England.[6]

The green birdflower is a perennial shrub that grows to about 1–3 m in height. It has hairy or woolly branches and dull green foliage. The oval leaves are about 30 mm long, the large and greenish pea flowers are streaked with fine black lines, and the club-shaped seed pods are up to 50 mm long. The plant's flowers grow on long spikes at the ends of its branches. The flower greatly resembles a bird attached by its beak to the central stalk of the flowerhead.[1] The Mauve flowers are partially covered in hairy lobes. Crotalaria cunninghamii is non-allergenic and its pods are large and almost square and are covered in a soft, green hairy shell.[3]

The appearance of the flowers of Crotalaria cunninghamii has been debated whether it resembles a bird by natural selection or if it is due to chance. The debate is whether the flowers are bird shaped to ward off unwanted predators or to attract certain pollinators, known as Batesian mimicry, or if it is just by chance that they look like birds and humans have associated the shape of the flower with a bird, known as pareidolia. Michael Whitehead from the University of Melbourne stated that the shape of the flowers are consistent with bird pollination, with its large flowers and long keel on its petals. This makes sense because the predominant pollinators of Crotalaria cunninghamii are nectivorous birds and bees.[7] There are a large number of plants with flowers that look like animals, such as the Dracula simia (monkey orchid) that looks like a monkey or the Phalaenopsis (Moth Orchid) that looks like a moth.[8] These plants have the same debate surrounding their unique appearance.

Crotalaria cunninghamii habitat is the arid to semi-arid zones to the tropics, including northern Western Australia, the Northern Territory, northern South Australia and southwest Queensland. Crotalaria cunninghamii predominantly grows in well drained soils in shrubland and grassland or savannah woodlands, usually on desert dunes, sandplains and drainage lines. Crotalaria cunninghamii also grows in Mulga communities in arid regions.[4] Mulga communities are 'hotspots' of resources such as water holes in deserts. Mulga communities account for 20% of the total land mass of arid Australia.[9]

There have been no reports of Crotalaria cunninghamii being toxic to humans, however, human toxicity has been seen in the Crotalaria genus. Many members of the Crotalaria genus are known to contain pyrrolizidine alkaloids, the most potent of which are monocrotaline, retrorsine and retronecine. Pyrrolizidine alkaloids are found in 3% of plants globally.[17] These alkaloids have a cumulative effect upon the body thus are completely safe if only small amounts are consumed. Many of these alkaloids have pronounced toxicity that has been known to decrease brain function, but the lungs and other organs may be affected as well. Mutagenic and carcinogenic properties of pyrrolizidine alkaloids have also been reported.[18] Pyrrolizidine alkaloids are known to alter vitamin A metabolism in rats, depressing plasma levels in livestock livers which can be fatal in some cases for animals.[19]

Crotalaria cunninghamii is usually pollinated by birds. During a study orchestrated by the Desert Ecology Research Group from the University of Sydney in 2011, it was found that during a period of unusually high rainfall in the Simpson Desert, rodents were observed eating and pollinating Crotalaria cunninghamii flowers. The rodents observed were the house mouse (Mus musculus) and sandy inland mouse (Pseudomys hermannsburgensis). There was a similar large rainfall in 2007 that this unusual phenomenon was compared to where there were no rodents observed. It was found that Crotalaria cunninghamii in 2011 had five times more inflorescences per plant, 90% more flowers per inflorescence and two to three times more nectar per flower, but the nectar was 30% less sugar rich.[20] Rodents accessed the nectar by chewing a hole through the calyx, as opposed to the way birds poke their beaks through the opening. The increase in the number of pollinators had a positive effect on the propagation of the species.[20]

The regular pollinators of Crotalaria cunninghamii are nectivorous birds, bugs and bees.[7] These creatures derive their energy from the nectar of Crotalaria cunninghamii and in return they pollinate the plant. The way they pollinate Crotalaria cunninghamii is by picking up its pollen when feeding from one male plant and when they go to a female plant some of that pollen falls into the female plant's stigma.[21]

The conservation status of Crotalaria cunninghamii is least concern. Possible threats to Crotalaria cunninghamii include habitat degradation. This species occurs predominantly on sandy soils which are easily eroded by rabbits, camels and other grazing animals.[10] Crotalaria cunninghamii has been recognised as an endangered plant in NSW according to the NSW Threatened Species Conservation Act 1995. NSW is the southernmost reaches of Crotalaria cunninghamii's range and hence struggles to propagate as it does everywhere else in its habitat.[22]

A general threat to flowers and plants in Australia is clearing of land for agricultural or other commercial uses. Crotalaria cunninghamii is not at high risk to land clearing for this purpose because it is confined to the Australian rangelands, which experience low rainfall and therefore have limited potential for development.[10]