Culture of Fungi Dependent (FD) Terrestrials

This is the last of the three terrestrial fact sheets in Culture Notes that NOSSA has produced on growing terrestrial orchids.  All three facts sheets can be downloaded – Click on the following for Fungi Dependent, Slow Multipliers and Fast Multipliers.

Orchid 1 Arachnorchis tentaculata

Arachnorchis tentaculata, common name King Spider Orchid or Large Green Comb Spider Orchid

FLAGBEARER SPECIES: Caladenia tentaculata (synonym Arachnorchis tentaculata)

Some 3/4 of Southern Australian terrestrial orchids are fungus dependent throughout their life cycle. Orchids that are fungus dependent have very specific cultural requirements. The fungus must be grown in the pot with the orchid. Sometimes a third entity such as a shrub or tree is involved in the fungal relationship.

A minimum disturbance culture is used.

Limited numbers are available each year. Other fungus dependent species are rarely available. Those in cultivation have mostly come from rescue digs in the past. NOSSA has started a seed kit project to help overcome this vacuum.

GROWTH HABIT: Australian ground orchids follow an annual growth cycle comprising 6 – 8 months as growing plants under cool (5 – 20°C max, 0 – 14°C min) moist conditions and 4 – 6 months as dormant tubers in hot dry (18 – 42°C max, 12 – 30°C min) conditions. The new tuber is produced in winter – spring. Each tuber sends up a shoot to the surface in Autumn and leaves grow rapidly in late Autumn/early Winter as temperatures fall and the rains set in. Sometime in October/November the leaves go yellow and then brown and dry as the days get longer, hotter and drier in late Spring.

LIGHT/SHADE: In Adelaide they thrive in a shadehouse of 50% shadecloth. Some species prefer heavy shade, others full sunlight, but most will adapt to a wide range of light intensity.

If the leaves and stems are weak and limp or if the leaf rosettes are drawn up to the light then the shading is too dense and the amount of light should be increased. FDs are mostly spring flowering and like higher light intensities at flowering time. flowers may have pale colours if placed in heavy shade, even temporarily, when buds are just starting to open.

In very cold areas an unheated glasshouse may be required for frost protection although light frosts do not worry the majority of species.

AIR MOVEMENT/HUMIDITY: All species like good air movement and will not thrive in a stuffy humid atmosphere especially if temperatures are high.

POLLINATION/SEED COLLECTION: FDs seldom multiply so must be propagated from seed.

Flowers on the strongest plants of the same species growing in pots are cross pollenated by hand to set seed pods. The flowers collapse in a day of so and pods ripen in 4-8 weeks. Pods are collected as they change colour from green to brown, which happens quickly on a hot day in October/November. Tea bags can be tied over the pods to catch the dust like seed if frequent visits to site are not possible.

Pods are stored dry in paper envelopes indoors over summer. Seed can be sprinkled on mother pots or scattered on bush sites.

SEEDLING CARE: Seedlings can be raised by sowing seed around potted mother plants.

At Easter time, just before the rainy season begins, the dust-like seed is mixed with fine sand in a pepper shaker (minimizes seed loss) and sprinkled on top of the pots and watered in. Germination occurs in Autumn/Winter as that is when the fungi are most active. Tiny leaves appear from July to October. The seedlings form miniscule tubers on droppers about 1 – 2cm below the surface. Seedlings take up to five years to reach flowering and are best left undisturbed until larger.

WATERING: The soil should be kept moist at all times during active growth by watering gently if there is no rain. Hand watering is especially necessary in spring as soil in pots dries out more rapidly than in the garden. Watering must be done slowly so that the mat of needles on the surface of the pot is not disturbed. Slugs and snails love these plants and must be kept under control. Raising the pots off the ground on galvanised steel benching is very effective in controlling these pests.

After the leaves have turned yellow, let the pot dry out completely to dry up the old roots and tubers otherwise they may turn into a soggy mouldy mess and rot may destroy the adjacent new tubers.

REPOTTING: The plants are not repotted but left in the same pot year after year.

SUMMER CARE: Keep the pots shaded and allow the pots to dry out between light waterings until mid-February when they should be set out in their growing positions and watered a little more often. The tubers of some species will rot if kept wet during the dormant period, others will produce plants prematurely which are then attacked by pests such as thrip and red spider and fungal diseases in the warm weather.

A thin layer of new leaf litter is placed on top of the existing leaf litter each summer to feed the fungus.  Chopped gum leaves or sheoak needles are suitable.

FERTILIZING: NO FERTILISER

OTHER CULTURE NOTES:

Advertisements

‘Tis the Season … for Dipodium

For many with Christmas and New Year holidays it is a busy time but not so with the orchids here in the Adelaide region.  The vast majority of orchids have finished flowering for the year except for a few including one of our most showy orchids, the Hyacinth Orchids (Dipodium species).  Of the four species found in South Australia, two are found in Adelaide Hills –  D. roseum or Common Hyacinth Orchid and D. pardalinum or Small-spotted Hyacinth Orchid and these will be flowering across the whole of the summer period.

Both of these Dipodium species are leafless plants that are dependent upon mycorrhizal fungi associated with stringy bark trees, either Eucalyptus obliqua or E. baxteri.  This growth requirement makes it impossible to grow in cultivation.  (Stringy bark trees can’t be grown in pots!)  The emerging stem and buds resemble an asparagus shoot.  The stems can range from a light green through to a deep dark red.  At this stage it is difficult to tell the two species apart although if there are yellowing tips on white buds it may be a clue that the plant could be D. pardalinum.

Once in flower D. roseum has a surprising range of variation  from carmine (a lightly purplish deep red) through to pink to white, with suffused rather than clearly defined spots.  On paler or white flowers these blotches may appear pale mauve-pink rather than candy-pink.   It always has a distinctive striped labellum.

Dipodium roseum composite

This feature sets it apart from D. pardalinum which has a clearly spotted labellum and in contrast to D. roseum, the flowers lack variation of colour but are consistently white with small well-defined candy spots.  (There are other Dipodium species with larger spots.)

Note the yellow staining on the bud and no stripes on the labellum

Note the yellow staining on the bud and no stripes on the labellum

And the final word, D. roseum is common but D. pardalinum is rated vulnerable in South Australia.

 

Reference: South Australia’s Native Orchids Bates 2011

The Role of Orchids

October is Orchid Month with the greatest number of species flowering throughout South Australia; so it is worth considering the role of orchids in the Australian bushland.  Hence this week’s blog is an article written by Belinda Newman, Western Australia.

Orchids: The Canary in the Coal Mine was published in the Friends of Kings Park magazine For Plants and People, Issue 70 p 22-24, 2010.  The article is both a good introduction to, and summary of, her 2009 thesis Orchids as Indicators of Ecosystem Health in Urban Bushland Fragments

Orchids: The Canary in the Coal Mine

Belinda Newman – Research Scientist BGPA

What could orchids and canaries possibly have in common?

Before occupational health and safety and ventilation systems were commonplace in the mining industry, a caged canary would be bought down to the coal seam by the miners.  Canaries are particularly sensitive to methane and carbon dioxide which made them excellent indicators for the build-up of dangerous gases.  A singing canary meant everything was fine, a dead canary spelt trouble and an immediate evacuation.

Although orchids can’t sing, they do possess a number of traits that make them sensitive ecological indicators.  The relationships that orchids have with their surroundings form part of a complex ecological web.  Orchids have specific relationships with mycorrhizal fungi, which they require both for germination of their dust-like seed and ongoing growth of plants in adulthood.  These fungi in turn rely on the appropriate soil moisture content and carbon sources.  Above ground, the majority of terrestrial orchids in the south west of Western Australia rely on pollinators for successful seed set.  For some orchids this plant-pollinator relationship has become so highly evolved that removal of the pollinator would spell the end of the orchid.  The pollinators also have specific requirements for habitat, appropriate food sources and nesting sites.  These above and below ground links to the ecosystem make orchids particularly sensitive to disturbances and changes in their surroundings.

The potential for orchids to be used as indicators of ecosystem health formed the basis of a study between Kings Park and Botanic Gardens and Murdoch University.  The coal seam was eleven urban reserves of varying condition on the Swan Coastal Plain.  The canaries were seven orchids common to Perth’s urban bushlands; the Carousel spider (Caladenia arenicola), Cowslip orchid (Caladenia flava), Pink Fairy orchid (Caladenia laitfolia), Pansy orchid (Diuris magnifica), Dark Banded Greenhood (Pteryostylis sanguinea), Purple Enamel Orchid (Elythranthera brunonis) and the Mignonette orchid (Microtis media).  Before it was possible to see which orchids made the best canaries, it was important to determine the health of each of the bushland sites.  A number of environmental variables were chosen that best reflected the health of the ecosystems.  Extensive surveys and analysis of species composition, plant functional groups against these environmental variables revealed a range of site conditions from close to pristine to highly degraded.  This provided the backdrop against which to determine the effectiveness of orchids as indicators through the measured responses of the orchid species.

Firstly orchid presence and abundance was measured across sites to determine if particular orchid species showed a preference for particular site conditions.  Diuris magnifica and Microtis media showed strong correlations and were most abundant in poor condition sites and Pteryostylis sanguinea showed strong correlations to sites in good condition.  While the abundance and presence of orchids appeared to correlate with site condition, we wanted to know what other aspects of the orchid we could measure as a means of judging the health of an ecosystem.

Successful seed set in plants reflects a healthy ecosystem and the reproductive success of the seven orchid species was investigated to determine the effects of declining site condition on seed set.  Pollination trials were set up to measure natural and artificial pollination events across all sites.  Widespread depression in pollination across all species and sites was found to be occurring, rendering seed set a poor measure of ecosystem health.

Investigations into the below-ground links orchids have with the ecosystem were undertaken by determining the presence and abundance of orchid mycorrhizal for the seven orchid study species across all sites.  Mycorrhizal distribution was found to be patchy within urban reserves and also revealed unoccupied niches capable of supporting orchid germination.  A greater abundance of Microtis media mycorrhizal at sites of poor condition supported earlier correlations of plant abundance at sites of poor condition.  The higher abundance of mycorrhizal symbionts for Caladenia arenicola at sites of very good condition also suggests its potential as an indicator species.

The study also looked at seedling growth in urban reserves.  This was the first time that biomass allocation in orchids has been investigated in light of ecosystem health.  In poor condition sites, Diuris magnifica and Caladenia arenicola increased growth effort to the above ground leaf. In sites of very good condition, these two species increased growth to the tuber to take advantage of being able to store starch as a result of both fungal and photosynthetic activity taking place.  Most importantly this shows a measurable change over a short period time.  Although it is effort intensive, planting orchid seedlings of a standardised size into the field may provide a useful and rapid measure of ecosystem health, much like caged canaries were used in the past.

This research into using orchids as an indicator species is the first of its kind and suggests that orchids can be used as an indicator of ecosystem health.  Future research will need to focus on the thresholds of the species identified as potential indicators in this study.  What aspect of the orchid’s ecology will give clear and repeatable data linked to ecosystem health?  Following the canary analogy, how long can orchids hold their breath? Future studies would need to focus on testing these thresholds.  The results of this study suggest that orchid presence and abundance, orchid growth and orchid symbionts can be used as indicators of ecosystem health, although work needs to be undertaken to refine the understanding of their response to specific disturbances.  This study provides a baseline for investigating the utility of orchids as indicators of ecosystem health in highly fragmented systems.  Perhaps orchids and canaries have more in common than first thought.