Wednesday, 21 October 2009

Sausage Tree needs Bats and Elephants


A lot of flowers are brightly coloured and scented, usually to attract birds, bees and that kind of thing. Most of the activity occurs during the day, with some flowers closing at night to avoid any further damage to their precious blooms.

But there are flowers designed for night time display. We have the Sausage Tree in flower right now, just south of the Henry Lawson gate. Its flowers are one of the more dramatic night-time offerings.

Kigelia pinnata, as it is called botanically, is a relative of the Jacaranda. Both are in the family Bignoniaceae with other garden plants like Wonga Vine (Pandorea), Cape Honeysuckle (Tecoma) and Indian Bean (Catalpa). They all have ‘foxglove’-like flowers, but are unrelated to Foxgloves…

As you can see in the picture, the Sausage Tree has a hanging group of flowers designed for bat pollination. The flowers are dark-blood coloured and smell offensive – the sort of thing big bats like. In their native habitat, but less commonly in the Royal Botanic Gardens, the large sausage-shaped fruits are eaten by rhinos and elephants, presumably spreading the seed far and wide.

As I wrote in Nature Australia a few years back (spring 2002): “Sweet-smelling, light-coloured flowers, often white or pale yellow and easily visible in the evening gloom, attract nocturnal insects. Moths hover over the flowers and, because they don’t need any platform to land on, these night bloomers often have neat, regular flowers. Jasmines, the so-called Night-scented Jasmine (Celestrum nocturnum), gardenias and the aptly named Moonflower (Ipomoea alba) are examples of this moth-pollinated clan.

“Another band of flowers emits a musty or rank odour at night. They are dingy in colour (greenish-yellow, brownish or purple) and often have dangly bits attached to the petals or other flower parts. They are the bat-attracters. Bats like something to hang onto—the dangly bits—and preferably with the flowers facing the right way—that’s upside down to us.

Look at the flowers of some of the tropical and subtropical garden plants such as the Sausage Tree (Kigelia pinnata), bananas, Cup of Gold (Solandra maxima), and the fantastically named Midnight Horror (Oroxylon indicum). A recent study revealed that some plants are even ‘loud’ to bats (see “Noisy Flowers”, Nature Australia Autumn 2000). The flower of Mucuna holtonii, a Central American vine, acts like a sound-reflecting mirror and draws bats to it. If the distinctive concave petal is removed, the flower cannot echo ultrasonic signals and remains unpollinated.

“Closer to home, flying-foxes pollinate or spread the seed of many Australian rainforest trees, undoubtedly playing a key role in the regeneration of some rainforest remnants. Eucalypts in these areas often have light-coloured flowers and produce more nectar at night apparently to attract these nocturnal visitors. Gliding and tree-climbing marsupials, with relatively poor vision but a well-developed sense of smell, are also active at night, but their role in dispersing the seeds of strong-smelling, dull-coloured fruits is unclear.”

So take a look at our Sausage Tree. Enjoy the flowers now and the sausage-shaped fruits in summer.

1 comment:

Ivan said...

Thanks for leaving a trace. It answered a question puzzling me for a while - it is Cestrum nocturnum that smells so sweet at night.