Download Arboretum Botanical Vampires! Parasitic and Carnivorous Plants in

Arboretum Botanical Vampires Walk (updated August 2010) www.mq.edu.au/arboretum Botanical Vampires! Parasitic and Carnivorous Plants in the Ecology Reserve This patch of bush consists of Hawkesbury Sandstone Vegetation with some riparian vegetation along the river. Would you expect to find parasitic and carnivorous plants here? Does it surprise you to know that you could find more than ten different species? But many of these plants are hard to find: some are ephemeral (short‐lived), some very small, a few grow high in the branches of trees and others are rare. Because of this the plants are not labelled or mapped ‐ you will have to hunt for them! Take a copy of the Field Guide to the Native Plants of Sydney1 with you, to help you. Parasitic plants Parasitic plants derive some or all of their sustenance, both organic compounds and nutrients, from other plants. There are over 4000 parasitic plant species in the world. Parasitic plants are either obligate parasites, which means they cannot complete their lifecycles without a host, or facultative, where a host is not essential to the completion of the plant’s lifecycle. Wholly parasitic plants, called holoparasites, do not produce chlorophyll and therefore cannot photosynthesise. Other parasitic plants do photosynthesise, but take water, nutrients and some organic material from the host or hosts, and these plants are called hemiparasites. Parasitic plants have modified roots, called haustoria, which invade the host plant and connect to the xylem, phloem or both to absorb water, organic compounds and nutrients. Parasitic plants can invade the roots or stems of their hosts. The plant parasites in the Ecology Reserve include trees, herbs and shrubs, stem and root parasites and hemi‐ and holoparasites. 1. Exocarpus cupressiformis (Native cherry, SANTALACEAE) Exocarpus cupressiformis, a small tree, is a root parasite. It is a hemiparasite on nearby Eucalypts. The plant is also unusual in that the flower stalks become larger and succulent at fruiting time, forming a hard green fruit on a tasty stem. The fleshy, tasty stalk attracts birds to eat the stalk and fruit and spread the seed. This method of attraction for seed dispersal differs from many other plants, which produce a tasty fruit around the seed as an attractant. Developing fruit on Exocarpus cupressiformis 2. Mistletoes (LORANTHACEAE) on Eucalyptus haemastoma Mistletoes are stem/branch parasites, and you may be able to spot some high in the branches of the scribbly gums (Eucalyptus haemastoma) by looking for a cluster of leaves that have a form and shape slightly different to the other branches and leaves. Three different mistletoe species can grow on this eucalypt including Amyema pendula, Dendrophthoe vitellina and Muellerina eucalyptoides2. Australian mistletoes have co‐evolved with the mistletoe bird, Dicaeum hirundinaceum, which eats the fruit produced by the mistletoes. The seeds pass quickly through the birds which digest the sweet fruit around it, leaving a sticky coat on the seed. When the birds poo, they wipe their bottoms on a branch, leaving the mistletoe seed stuck in a perfect spot to grow a new plant, high in the canopy! 3. Cassytha glabella and C. pubescens (Devil’s twine, CASSYTHACEAE) Parasitic plants can be generalists, parasitising multiple species, which may include several hosts at the same time. Cassytha is a generalist parasite and can be seen sprawled across several plants. Species in the Cassytha genus are hemiparasitic vines. Soon after a Cassytha plant germinates, its shoot (which initially contains chlorophyll) swings around in the air until it touches another plant. Then haustoria form and once the Cassytha can obtain sap from the host, the part of the plant that is rooted in the ground dies off and the plant becomes a holoparasite3. Two species of Cassytha may be found here, the hairy and warty C. pubescens, and C. glabella which has much thinner stems Cassytha glabella with hausteria (top left) and fruit (bottom) visible 4. Olax stricta (OLACACEAE) Olax stricta is another root parasite. It is a slender erect shrub that occurs in heath and woodland on sandstone, but it is not abundant and may not be easy to find. Parasitism results in harm to the host and may often limit the density of a host plant. A parasite must remain in balance with its host to minimise the risk of damaging too many hosts at the one time. Such impacts may limit the number of available hosts for the parasite in the future. 5. Choretrum candollei (Snow Bush, SANTALACEAE) There are three plants in this area from the SANTALACEAE family which are all root parasites. Choretrum candollei is rare here, but is recognisable by its angular stems and lack of leaves. It is a shrub that grows to 2 m tall. In the spring and summer this species produces an abundance of racemes of small, white flowers which produce an overpowering, sweet smell. 6. Leptomeria acida (Acid drops, native current, SANTALACEAE) Leptomeria acida is the final member of the Santalaceae family found here, together with Exocarpus cupressiformis and Choretrum condollei. It is a shrub that grows to 2 m high and a root parasite. Similar to the Exocarpus, this species has leaves that are reduced to scales. Its stems are triangular in cross section. Leptomeria acida produces edible fruits that are very acidic and high in vitamin C1. 2 of 4 7. Cryptostylis erecta and C. subulata (Slipper orchids, ORCHIDACEAE) Some plants derive some of their nutrients from mycorrhizal fungi. These are called myco‐heterotrophs rather than parasites as the plant provides carbon to the fungi in return. Many orchids are myco‐
heterotrophs. Cryptostylis erecta (hooded orchid) and C. subulata (large tongue orchid) grow in the Ecology reserve. For much of the year, these orchids appear as a single leaf growing from the ground, with C. erecta leaves easily distinguished by a purple underside. In spring a long stem produces several flowers which are pollinated by male wasps which mistake the flowers for female wasps. This pollination strategy is called sexual deception. The orchids produce dust‐
like seeds and with almost no reserves stored Cryptostylis erecta in flower (left) and leaves (top in the seeds, young orchid plants are right) and the leaves of C. subulata (bottom right). dependent on the mycorrhizal fungi. Carnivorous Plants In contrast to parasitic plants, carnivorous plants acquire some of their nutrients, but not energy, from animals or protozoa. They do not acquire organic molecules from their prey which means they still need to produce chlorophyll to photosynthesise. Nitrogen, obtained from the amino acids in the insects’ bodies, is one of the most important elements acquired in this way by the plants. There are over 600 species of carnivorous plants worldwide. 8. Drosera peltata (Sundew, DROSERACEAE) You may find Drosera peltata growing in damp patches of ground . These small herbs have leaves in a rosette on the ground and a long, erect stem with stalked crescent shaped leaves. All leaves have reddish glandular hairs each with a drop of clear, sticky liquid on the end. Small insects become trapped in the sticky liquid. After a capture, the leaves roll up enclosing the insect which is dissolved and digested, providing the plant with nitrogen, an element often lacking in the sandy soils they inhabit. Drosera peltata also photosynthesises and absorbs nutrients through its roots, so the insect meals can be considered as supplements. Droseras are very attractive plants, both because of the pretty flowers and their The insect catching leaves of Drosera peltata. glistening, colourful leaves. 3 of 4 9. Stylidium graminifolium (STYLIDIACEAE) Stylidium graminifolium is a perennial herb that can be found all year round. Look for the flowers, as species in the genus Stylidium have a very unusual mechanism for pollination. Two anthers and the style are fused together on an elastic stalk which is normally bent back behind the flower. When the centre of the flower is touched, usually by an insect attracted to the flower by the attractive petals, a trigger releases the style and anthers, which flies forward, showering the pollinator with pollen or collecting pollen from a previously showered insect. The trigger resets itself. You can trigger the mechanism by gently inserting a small twig into the middle of the flower. There are over 140 species of Stylidium, mainly Australian, and they are commonly called trigger plants. In addition Stylidium species are carnivorous with glandular trichomes on the flowers and scape which can catch and digest small insects4. Stylidium are better known for their triggered pollination mechanism than for their carnivory. 10. Utricularia species (LENTIBULARIACEAE) Right down by the river or small tributaries, you might be lucky enough to find some Utricularia plants. These are carnivorous plants like Drosera and Stylidium, but use a different mechanism to capture food. Microscopic organisms from the water are captured by modified leaves that grow from low down on the stem. The leaves form small bladders ending in tufts of hairs. These suck in small amounts of water and organisms from the water. When the captured organisms are digested, the trap resets itself. There are several species of Ultricularia that may occur here including U. biloba, U. dichotoma, U. gibba, U. laterifolia, U. uliginosa and U. uniflora. Conclusion What a range of parasitic and carnivorous plants in this little patch of bush! Why are there so many? The sandy soils derived from Hawkesbury Sandstone are very poor in nutrients. They are particularly low in phosphorus, but also in nitrogen5,6. Carnivory and parasitism in plants are considered adaptations to low nutrient soils as they provide an alternative method of acquiring nutrients to absorbing them through normal plant roots7. This is one explanation as to why there are so many carnivorous and parasitic plant species here. Can you think of any others? The species list was developed by Alison Downing and the text and photos by Julia Cooke, both from Biological Sciences. 1
Robinson, Les. 2003. Field Guide to the Native Plants of Sydney. 3rd Edition Downey, P. 1998 Cunninghamia Vol. 5(3): 685‐720 3
Hamilton, A.G. 1914. The Flora of the South Coast. Handbook for New South Wales, British Association for the Advancement of Science. 4
D. W. Darnowski, D.W. et al. 2006. Plant Biology 8: 805–812 5
Hannon, N.J. 1956. Proceedings of the Linnaean Society of NSW 81:119‐142 6
Beadle, N.C.W. 1962 Ecology 43(2): 281‐288
7
Adamec, L. 1997 Botanical Review 63(3): 273‐299 2
4 of 4