Orchids

By John Moye

The Orchid Flower

What makes an orchid flower different from those of other flowering plants? In all flowering plants the flower is the vehicle of reproduction. In some, flowers may be either male or female (eg pumpkins), and in some other instances, the entire plant may be either male, producing only pollens, or female with seed producing structures (eg casuarinas).

However, most of the flowering plants have flowers which have both male and female components within their structure. Orchids belong to this group, but differ from other members by having both male and female components contained within a single structure called the column. This is the essential difference between orchid flowers and those of other flowering plants.

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These differences are illustrated here:

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FLORAL STRUCTURES

 

Orchid flowers are often showy and highly specialised for insect pollination. Consequently, floral parts of the flowers of the various genera have evolved to facilitate this.

In our native orchids there is as wide a diversity in this floral form as there is within the insect pollinators, such that it may be difficult to recognise some parts without close examination.

It is this diversity of form, however which provides the mystique which surrounds them, and the fascination by enthusiasts the world over.

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Orchids as flowering plants

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Orchids are considered to be the most advanced family in the Monocotyledoneae.

This group of plants also include Gramineae (grasses), Liliaceae (lilies), and Iridaceae (iris).

Some regard the Orchidaceae to be the most advanced of all flowering plant families.

As Monocots, orchids have one seed leaf (cotyledon), generally marked parallel leaf venation, and six floral parts.

Growth forms

SAPROPHYTES: Leafless plants which derive nutrients from decaying organic material or through some mycorrhizal association with other plants. Pseudovanilla foliate, Epipogium roseum, Dipodium variegatum are some local examples.

LITHOPHYTES: Typically plants which grow on rocks, eg Dendrobium kingianum, the Pink Rock Orchid (photo right).

EPIPHYTES: Plants which grow on trees but which are not parasitic, eg Dendrobium aemulum (Brushbox orchid). Many epiphytic orchids may also grow on rocks as those in the Dendrobium speciosum complex.

TERRESTRIALS: Those which grow in the ground, eg Greenhoods, Flying Ducks, etc. There are a few genera which have both terrestrial and epiphytic species, eg Liparis.

Orchids in Australia

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Although there are up to 1000 genera and between 25,000-35,000 species throughout the world, Australia has only 193 genera about 1300 species. However, 95 per cent are endemic.

Eighty-two per cent of Australian orchids are terrestrials (Jones, 2006).

On the North Coast, Archer (1964) listed 106 species – 67 terrestrials, 49 epiphytes. Steenbecke (2000) lists from the Clarence-Tweed catchment areas 174 species of which 121 are terrestrials.

Orchid Habitats

Orchid seed is minute and is usually transferred by wind. As seeds consist of an embryonic sac only, and without endosperm, they rely on a compatible mycorrhizal interaction to initiate germination and assist in the early growth stages. Orchid seeds germinate and plants grow best in relatively undisturbed areas.

Here, on the Far North Coast, orchids can be found growing in most ecosystems from coastal sands through to rainforest remnants, and at all altitudes.

Many species have specific growth requirements. For example, Phaius australis (photo right) is generally a plant of lowland Melaleuca swamps. Dendrobium melaleucaphyllum is most commonly associated with Melaleuca styphelioides also in coastal swamps, Dockrillia cucumarina is found almost always on trunks and limbs of large River Oaks (Casuarina cunninghamiana) inland from the coast and sometimes west of the Great Divide.

While most orchids show a preference for sheltered situations, some species may be found growing in open sites. Several species are known to grow in open situations exposed to full sunlight, eg Caleana major, Pterostylis bicolour, and Microtis sp. within the Wardell cemetery.

The species Spiranthes sinensis has been seen growing roadside, adjacent to sporting fields and even urban lawns. Three species, Pterostylis curta, P concinna, and Microtis sp have been recorded from one urban lawn in the Lismore area. A large plant of Dockrillia linguiformis may be seen growing on a large Eucalypt roadside in Brunswick Heads.

Two mature plants of Geodorum neocaledonicum have been recorded from recent dunal systems in the Lighthouse Beach area at Ballina. The species Bulbophyllum minutissimum is said to grow on boulders on coastal headlands, mangroves, as well as colonising on old and isolated Moreton Bay figs.

In summary, while most orchids occupy their preferred ecological niche, many species may sometimes be found in disturbed areas including those often infested with exotic plants.

Orchid names

Until about 25 years ago, orchid research in Australia was largely at an “enthusiast” level which sometimes resulted in confused identification and irregularities in naming of some species.

In recent years, the professional botanists David Jones and Mark Clements, Centre for Plant Biodiversity Research, CSIRO, Canberra, have been active in native orchid research nationwide, and endeavouring to systemise orchid nomenclature. Their work has been widely published in appropriate texts during this time.

The volume “Native Orchids of Australia” D.L.Jones, 2006, formalises this work.

Many will view this new publication with skepticism and already one article emanating from the School of Botany, University of Melbourne, seems to be challenging the work of Jones as it relates to the Dendrobium speciosum complex.

Throughout the above I have used the names given to orchids as used in Bishop’s Fieldguide for simplicity.

Some References

NATIVE ORCHIDS OF AUSTRALIA, David Jones, 2006 is the most recently published book. While Bishop’s FIELDGUIDE TO THE ORCHIDS OF NSW AND VICTORIA is a useful volume it may now be out of print.

Greg Steenbecke’s web site North Coast Orchids and the NSW Herbarium’s NSW PlantNET are handy references (after ‘Search’ type in “Orchidaceae” for complete list). Both contain brief descriptions, and in some cases photographs.

Some earlier published texts may sometimes be found as book sale items, or listed on eBay.