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Short Cuts

Readers are invited to submit short items of interest about Australian plants to be included here. If submitting non-original material (eg newspaper or magazine cuttings), please also advise if the author has given permission to republish and, if not, please provide a contact address so that permission can be sought.

Short Cuts in this issue:

Ants: Good or Not-so-good in the Bush?

These small creatures can have unexpected impacts on plant regeneration.

Symphionema

Not well known....but definitely worth a try!

The Orchid Which Catches Stingless Bees

Native bees play an important part in pollination.

Hibbertia - You Light up my Life

Guinea bushes can add colour to any garden.

Pruning Australian Native Plants

To Prune...or not to Prune. That is Indeed the Question!

Sheer Exhilaration!

Successful Growing of Sturt's Desert Pea does not Necessarily Involve Black Magic....

Ants: Good or Not-so-good in the Bush?

Ants are a darn nuisance, or worse, when one is sitting eating lunch in the bush or looking closely at a terrestrial orchid. They are certainly not-so-good for us. But what about the plants? Is their survival aided or hindered by ants? According to observations over the past 20 years, they aid some plants and disadvantage others.

Some ants aid the dispersal of plants by moving their seeds well away from the parent plant. This dispersal mechanism, called myrmecochory, is very widespread in the Australian flora, with at least 1500 species having their seed dispersed in this way. A little observation in the bush in spring will soon show ants lugging seeds larger than themselves away from the shrubs that produced the seeds. How obliging; how kind; how unselfish, how altruistic. Or is it? Not likely. The ants are in it for what they can get out of it - food.

The ants are after the oil bodies (elaiosomes) that are attached to these seeds. These structures, which in acacias are called arils, are rich in oil. Worker ants take the seeds back to the nest, where the elaiosomes are removed and fed to the larvae. The seeds can be taken up to 15 metres from the tree that produced them. Other workers then remove the seeds from the nest and bury them in the surrounding soil.

An interesting recent finding (Functional Ecology Vol. 8, pages 358- 365, 1994) about elaiosomes is that they contain chemicals that are similar to some that are found in insect blood. As soon as carnivorous or omnivorous ants get near an elaiosome, their biting and holding mechanisms are activated by the chemicals, as if the elaiosome were an insect. The ants have no choice but to grab the elaiosome, with its attached seed - so long as the elaiosome is of the right colour - and take it back to their nest. (the elaiosomes of Western Australian plants are white, so WA ants only respond to white elaiosomes.) The harvesting and burying action of ants rapidly removes seeds that have been shed from myrmecochorus plants, so removing them from the clutches of other seed harvesters who use the whole of the seed as food.

In contrast to what has just been described, the harvesting of eucalypt seeds by ants can prevent regeneration. According to observations by Yates, Taplin, Hobbs and Bell (Australian Journal of Botany vol. 43, pages 145 -155, 1995), such harvesting is the main reason why Eucalyptus salmonophloia (Salmon Gum) is not regenerating in remnant stands in the wheat belt of Western Australia. There is a continual rain of viable seed from these trees to the soil, but their short period of viability, combined with destruction by ants of a large proportion of the shed seeds, means that there is essentially no regeneration of these magnificent trees in roadside populations. In unfragmented woodlands, regeneration often occurs after drought, fire or flood. The death of the tree canopy caused by these events releases a massive drop of seeds, which satiate the local ants, so that at least some seeds survive to germinate.

From the August 1996 issue of the "SGAP Journal", newsletter of the South Australian Region of the Society for Growing Australian Plants.

Symphionema

Amongst the lesser known genera in the family Proteaceae is the small genus Symphionema, with two species confined to New South Wales. The genus was named by Robert Brown in 1810 and received its name from the manner in which the slender filaments of the stamens are united around the style (Greek sumphuo, I unite; nema, a thread).

Both of the species of Symphionema are small undershrubs, somewhat of an herbaceous appearance; the leaves are divided into a number of small pointed segments. The small, white to cream flowers are tubular in bud and then split into four spreading segments, to which the filaments of the stamens are attached; the united filaments of the stamens often split as the segments spread. The flowers, which grow in slender terminal spikes, have a small 3-lobed bract at the base which persist after the floral segments have fallen and surrounds the small nut-like fruit. Both species flower in spring.

Symphionema montanum

This species is an erect shrub 0.5 to 1 m in height, with several stems arising from ground level. The small parsley-like leaves are divided into a number of segments, each of which is further subdivided into three or more flattened segments, terminating in short, pointed apex. The small, creamish-yellow flowers, 3 to 4mm long, grow in terminal spikes, 25 to 40mm in length. The fruit is oblong to egg-shaped. Symphionema montanum occurs on the higher parts of the Blue Mountains and the Woronora Plateau, west and south of Sydney respectively, where it occurs on heathlands in soils derived from sandstone. In the more exposed, colder parts of the Blue Mountains, the leaves of this species become reddish-brown during cold weather.

Symphionema montanum is common in moist heathland in the upper parts of the Blue Mountains west of Sydney. Select the thumbnail image or plant name for a higher resolution image (31k).

Symphionema paludosum

Closely allied to Symphionema montanum this slender, spreading to straggling plant, differs chiefly in its more slender straggling habit of growth and the small leaf segments being almost terete. The tiny creamish flowers are more slender and occur on the spikes about 20mm long. Symphionema paludosum occurs in the coastal areas north and south of Sydney, where it grows on moist heathlands chiefly in soils derived from sandstone and of a peaty nature.

Growing Symphionema

Plants may be raised from seed or cuttings. Seeds are not usually available, and, for those who live near where the plants grow, it is necessary to keep them under close observation to collect seed, as they fall from the plant when ripe. The seed germinates slowly and seedlings require several years to flower.

Propagation is readily carried out using cuttings of hardened new growth. The resultant plants may flower within 12 months to two years after potting on the rooted cuttings. Under cultivation a sandy, peaty-type soil gives the best results in a protected position with regular watering.

From the March 1986 issue of "Australian Plants", the journal of Society for Growing Australian Plants.

The Orchid Which Catches Stingless Bees

The delightful fragrance of the small yellow flowers of the bush orchid Dendrobium monophyllum attracts a wide variety of insect visitors.

Flies, commercial bees and larger native bees hover briefly near the flowers before flying away. However, the miniature stingless native bees (genus Trigona) are the only confirmed pollinators.

Trigona workers are small enough to crawl right inside the 8mm wide flowers. They appear to get trapped inside as they spend 20-30 minutes inside each bloom! They get caught in an awkward head-down position and struggle back and forth trying to escape. Finally after many attempts they find that if they slide sideways, arch their body and do a reverse wiggle, they can get free. However, by this stage the orchid's pollinia (bundles of pollen) are glued firmly to the back of the bee's thorax (mid section). The orchid's fragrance must be a good attractant for these bees because before long the bee enters yet another bloom, transferring the pollinia to the second orchid's stigma and the pollination process is complete.

Pollen from this orchid is bound up into tight bundles which bees cannot use for food. This orchid also does not produce nectar inside the flower. So the bees do not get any obvious reward from entering the flower. Nevertheless Trigona are attracted by the flower's scent and appearance and also collect some nectar which is secreted outside the bloom near the stalk.

Dendrobium monophyllum orchids grow on boulders and trees in humid open forests or rainforest margins from Cooktown to Grafton. Tad Bartareau discovered the importance of Trigona to this orchid's pollination during a study on the Atherton Tablelands. However, Tad found that pollination rate of Dendrobium monophyllum was poor if the orchid plants were widely separated. He did some hand-pollination experiments which showed that this orchid does not set seed capsules unless the pollen it receives is from a different plant. So the visits of the Trigona to isolated orchids were largely wasted because they were usually carrying pollinia from the same plant.

Tad is now continuing to study the pollination activity of Trigona carbonaria in this region for his PhD project at James Cook University.

From the 'Fascinating Pollinators' column in "Aussie Bee" (Issue 2). This regular column presents the latest research about the interactions of native plants and native bees. A free copy of "Aussie Bee" is available on request (limit one copy per family) from: Australian Native Bee Research Centre, PO Box 74-P1, North Richmond NSW 2754.

Hibbertia - You Light up my Life

According to Gardner's book, Wildflowers of Western Australia, there are 64 species of Hibbertia in WA alone. All except two species have yellow flowers. Most of those from WA are shrubby bushes. He says: "Members of this family are easily recognised by the five free concave persistent sepals and the five, usually notched deciduous petals which fall early; the usually numerous stamens - and the almost free carpels, commonly two or five in number, which open outwards to liberate the seeds."

The common name for Hibbertia is "Guinea Flower", from the golden pre-decimal coins called 'guineas'. (The flower of H.scandens really is as big as a 'guinea'.) Hibbertias well deserve this name, as they look like pieces of sunshine lying on the ground and light up the shady places under trees and leggy, bare-ankled bushes. They are a perfect species to add to a garden, about five years down the track, to give it a lift without having to totally change everything.

Hibbertias are really understorey plants, although a few will grow in very sunny positions. Most are not fussy about soil type, but none like a soggy root system. This need not be managed by raised beds but by siting the small plants among already established shrubs, where competition for water will keep the Hibbertia on the dry side and provide the necessary cover at the same time.

Hibbertia pedunculata is a ground-covering plant which self-layers. It shows the typical "buttercup" shape of the flowers. Select the thumbnail image or plant name for a higher resolution image (23k).

I've always had some hibbertias. H.scandens found a congenial home inside a Melaleuca where it is sheltered from frost. Individual "arms" may reach three metres. The prostrate green form of H.obtusifolia will root at the nodes in damp litter, and reached over a metre wide. H.empetrifolia (syn. H.astrotricha), facing east against the back fence under a Callistemon, took off like a rocket and the next year smothered itself in flowers. H.procumbens was slow to take off because of the raw tanbark we spread as mulch. This soon was impenetrable to water as it matted together with a white fungus. We scraped this back and covered the bare soil with stone chips for a mulch. The Hibbertia still lives and is happily warming the feet of a Calytrix. It roots at the nodes if encouraged with moist humus and has reached a metre wide. In Canberra it flowers from late spring to early summer and can withstand dry periods once established.

The stunning WA plant H.stellaris is definitely a 'fuss pot' but could be treated as an annual. Two colour forms available are the regular 'orange' and a bronzy gold form which could be described as 'early season mandarin'. For both H.serpyllifolia and H.cuneiformis it was difficult to achieve the right balance between the amount of overhead cover and watering.

I decided to outline a 'path' with prostrate gold plants to complement a Senna, Chrysocephalum semipapposum, Acacia wilhelmi, and the gold in the Hakea victoria leaves. Along with Goodenia spp., Vellia spp. and Chrysocephalum apiculatum, I put in Hibbertia microphylla, another WA species having small round leaves with recurved edges that tend to hang downward along the stems. It can grow to 60x80 cm and so far it's doing well on a weekly watering. Cuttings strike easily. Another plant tried was supposed to be H.humifusa, a prostrate plant from the Grampians in Victoria but, from its response to conditions, was probably H.fasiculata.

I have begun planting the pool surrounds and have included a local H.obtusifolia of upright grey form. This is one very tough plant that grows on dry, stony hillsides. While it grows easily from soft tip cuttings, getting these soft cuttings is not easy. The plant puts them out irregularly, in response to good water supply. Not only do you have to be there at the right time - but you need to have beaten the kangaroos as well. The local H.obtusifolia varies in colour from lemony gold, through yellow, gold, buttercup to the orange side of gold, and flowers range in size from five to ten centimetres. Old plants may be up to one metre in diameter. Can you imagine how splendid an informal hedge of them would be in early summer?

These plants are really attractive and deserve to be grown more. Someone else besides me must have some bare-bottomed bushes needing brightening up, or a corner needing colour.

From the December 1997 issue of the newsletter of SGAP's Canberra Region.

Pruning Australian Native Plants

In the past, many gardeners believed that native plants, particularly those in informal bush gardens, shouldn't be pruned; after all, Mother Nature doesn't own secateurs or a pruning saw. Actually, Nature has her own "pruning tools"; in the bush, plants are "pruned" by insects, animals, fire and the elements.

Why do we prune?

Pruning can be a means of improving the appearance of a plant, for it will encourage the plant to branch and thicken. The shape and size of a plant can be controlled by pruning. Pruning can also be used to repair a damaged plant. Pruned material can be used for cuttings.

When should pruning be done?

Generally speaking, pruning can be done when it suits you. However, if possible, pruning should not be done after the flower buds have formed.

How hard should plants be pruned?

Most Australian native plants should not be pruned back to bare wood. There should be some healthy foliage left on every branch or stem that is shortened. The hormones that are present in the lower part of the stem will then be activated to encourage branching.

Some exceptions to the above rules

• Callistemons can be pruned back to bare wood, for they have dormant buds, which are activated if the plant is pruned hard.

  This Callistemon shows vigorous regrowth after being pruned to near ground level. Select the thumbnail image or plant name for a higher resolution image (48k).

  
  

• Some eucalypts (such as E.caesia) can be chopped off at ground level every 5 years or so. The cut should be made just above the swelling at the base of the trunk. The swelling is made up of undifferentiated plant cells which can then develop into buds. In the wild, this mechanism allows the tree to survive and recover from the effects of a bushfire. When the regrowth is about 1.5 metres high, chop off the strongest leaders (they tend to have a weak junction to the swelling) and allow about 3 other shoots to take over.

• In a garden situation, plenty of water and reduced insect attack means that, without some intervention by the gardener, most mallees will produce only one stem. This very dominant stem tends to suppress other stem buds. To encourage multiple stems, all mallees can be chopped back. However, some species and cultivars may be slow to recover from a hard prune. For example, E.erythrocorys can be cut to about half size every year. If, however, it is cut to the base, it may not flower for several years.

From the August 1996 issue of the SGAP Journal of the South Australian Region of SGAP.

Sheer Exhilaration!

If my limited experience south of Brisbane, some ten km from the coast, is any guide, growing Sturt's Desert Pea, Swainsona formosa, in situ is not difficult - as long as uncontrollable weather conditions are favourable. This is no report of a careful experiment. I did no more than list a few obvious factors, then put them unmodified into reasonably successful practice for three seasons - beginner's luck, if you will!

The most important of the controllable parameters include seed viability and vigour, sowing time and method, site selection and preparation, and nurture of the maturing plant. Every effort should be made to obtain fresh seed. Viability can be low under the best of conditions, despite assurances that Swainsona seed does not deteriorate in storage, it certainly does!

Sturt's Desert Pea, Swainsona formosa is one of Australia's most spectacular wildflowers and is the floral emblem of South Australia. Select the thumbnail image or plant name for a higher resolution image (59k).

I soak the seed in cold water overnight. The minority that do not swell may be soaked safely in hot water to increase the yield. I then sow it all in pure medium sand, one seed per cardboard cylinder, at least 10 cm long. Germination occurs within three to ten days. However, this does not seem to be a reliable index of vigour. Even some of the earliest seedlings can just "sit there". So I select the most vigorous within one week of planting out. Normally, the length of the cylinder will ensure that the tap root does not reach the bottom in that time, so planting is virtually in situ.

Sturt's Desert Pea seems to require a well-drained sandy loam at least half a metre deep and 10 sq metres in area in full sun, with no special nutrient demands. However, I always sprinkle this area generously with lime before sowing, and water it well in. I plant three seedlings centrally by easing their cylinders into holes drilled in the wet soil with a plastic pipe. The cylinders can then be removed carefully, though this does not appear to be crucial to healthy growth. Once the plants begin to run, they can be thinned down to the healthiest.

In this near-coastal, subtropical climate, failure even of the best specimens finally occurs through excessive rainfall or humidity. Flowering may not occur, therefore, if planting is delayed until spring. I set my seedlings in place by late autumn, protecting them from winter frosts. Come spring and they have enough head start, except in abnormal weather, to flower and even seed before the summer stress.

Despite its arid origins, Sturt's Desert Pea does require regular watering in my well-drained garden. I have found it adequate, though, to confine this to some three litres per month applied at once to the base of the centre of the plant. But if yellowing of leaves is noticed at any time, this could mean that the plant requires immediate attention.

I will be pleased if these few thoughts assist other enthusiasts to experience the sheer exhilaration which the blooming of this spectacular species brings to those fortunate enough to share its space.

From the December 1997 issue of "Australian Plants", the official Journal of the Society for Growing Australian Plants.

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Australian Plants online - September 1998
The Society for Growing Australian Plants