Oceania Orchids
Darryl and Alison Smedley

Review of the Distribution, Reproductive Biology and Morphology of the Natural Hybrid Dendrobium X suffusum

By Darryl Smedley dsmedley@ozemail.com.au

(This article originally appeared in The Orchadian Vol.12 No.2 December 1996)

INTRODUCTION

The natural hybrid between Dendrobium kingianum and D.gracilicaule was originally described as D.suffusum by Leo Cady in 1964 (Cady 1964). The type plant was found growing on North Brother Mountain at Laurieton NSW in September 1961.

This article will attempt to relate in one place as much information as it was possible to gather on the dozens of plants of the hybrid between D.kingianum and D.gracilicaule that have now been collected. What follows is necessarily incomplete. Plants are still being located and no doubt will continue to be discovered in the future if enough of the parent plants and their habitat remains undisturbed. Unfortunately, much data on the discovery of many plants has been lost due to the appalling neglect of the need to keep basic data on plants from a known wild source. Nevertheless, the article will attempt to collate all known information on the taxon’s occurrence in the wild. I will also discuss nomenclature, distribution, reproductive biology, vegetative characteristics and floral morphology.

Cady (loc. cit.) gave the plant discovered on North Brother Mountain the name D.suffusum and made no mention of any possible hybrid origin. He mentioned only its resemblance to D.gracilicaule in vegetative characteristics and to D.kingianum in its floral morphology. In an editorial immediately following the description of this species, caution was recommended concerning description of a new species based on a single example or where its occurrence is known only to be casual. Doubts were also mentioned about its validity as a true species but the editorial also did not speculate on a possible hybrid origin for the taxon.

The next reference to the orchid after the original description appears to be in the Proceedings of the Fifth World Orchid Conference (Upton & Clemesha 1967). Here, the hybrid origin of the orchid was recognised but the citation still appeared as D.suffusum.

The addition of the capital letter 'X' between the generic and the specific epithet is the established practice for recognising hybrids of natural origin and is in accordance with the International Code of Botanical Nomenclature (Greuter et al 1988).

However, in the case of an orchid first described as a species and subsequently recognised as a natural hybrid, there is no formal method for altering the citation. It is curiously left to become a matter of common usage or practice. Thus we now have D.X suffusum (first used by Dockrill, 1969) instead of the original D.suffusum. Given the strict controls on nomenclature in the Code, the method of acceptance of the change is most odd.

DISCOVERY

Mr. Alan Willows, a long time resident of Laurieton NSW (the town at the base of North Brother Mountain) is generally credited with the discovery of the type plant of D.X suffusum. My research has uncovered this not to be the case. Cady (loc. cit.) did not actually cite Willows as the finder of this orchid, the original reference is "North Brother Mountain area NSW per Mr A.Willows" (my emphasis). A misconception of this credit has been perpetuated to the point where authors are now acknowledging Willows as the finder (Upton 1989).

In September 1988 I had the opportunity of an afternoon's ramble with Alan Willows in his garden at Laurieton. We discussed the origin of the type plant and I learnt the proper facts of its discovery. I have to place on the record that the type plant was actually found on the mountain by another Laurieton resident by the name of McCoy, who gave it to Willows. Willows takes no credit for its discovery, apart from being the medium by which it was brought to botanical and horticultural notice. At the time the Laurieton plant was located there were at least two other plants of D.X suffusum in cultivation. Both these plants, Nos. 52 and 53, were found at Cloud Creek, Nymboida in 1954 and 1955 by parties which included Mr.Ken Russell of Dungog NSW.

From June 1988 to September 1989 I gathered information on D.X suffusum by way of a literature search and by personally following information on its occurrence by letter or telephone. A request for information published in The Orchadian (Smedley 1988) elicited only two responses. Details of the plants of this natural hybrid about which some data are known are presented in Table 1. (NOTE: Table 1 not included in web site).

There are 58 plants recorded in Table 1 but I can give no guarantee that each plant cited is a separate clone. The data on the occurrence of some is very meagre. It is more than likely that some plants are repeated. It became very disappointing whilst gathering the data to find that very little care was often taken by finders and growers to record and maintain original collection data. Many times I was told a particular clone was found "in the mid sixties", "early seventies" etc. making it impossible to cross-check the fidelity of separate plants. Notwithstanding this, the information recorded in Table 1 represents considerable expenditure of effort. Apart from other natural hybrids where only one, or a few clones are known, I believe it represents the most comprehensive data set on any Australian natural epiphytic hybrid yet compiled.

By the time of the publication of Australian Indigenous Orchids Vol.1 in 1969, three plants of this hybrid were known to the author, Alick Dockrill. There is no doubt that many others had been located and were in cultivation, (e.g. Nos.25, 52 and 53), but these other plants had not been formally recorded. Dockrill (in litt. 14 Dec.1988) unfortunately can give no information on the two additional plants recorded in Australian Indigenous Orchids. He was advised of their existence by the late Len Archer and did not press for additional information at the time.

Mr.Roy Gifford of Erina NSW (pers. comm.) said that Archer kept a comprehensive loose leaf register of all his collections of note. I attempted to locate this document, without success, as I believed it could complete the data on the other plants from Laurieton and the "Upper Clarence" mentioned by Dockrill. It would also probably have data on the mysterious plants, Nos.16-23, presented to the Royal Botanic Gardens, Sydney by Archer in 1981. The staff at the Gardens were unable to locate the register and the Garden's Accessions Register is regrettably silent on much of the collection data for these plants.

Betts (1984), in Archer's obituary, recorded that many of Archer's pressed specimens were donated to the herbarium of the Botany Department of The University of New England. The curator of the University Herbarium, Dr.Gordon White, advised (in litt. 13 Sep.1988) that no Archer orchid specimens could be located there, nor do they have the elusive register. They have a few Archer collections, only Acacia spp.

It is worth recording that Archer informed Gifford that a total of seven plants of D.X suffusum were discovered on North Brother Mountain. I have not been able to confirm this from any other source.

References to D.X suffusum in the orchid literature are comparatively scarce. Most citations are in passing in articles on other topics (Corrigan 1987, Gregory 1982) although some articles provide tantalising information (Barnham 1982, Gregory 1977).

For many years after its description, D.X suffusum was regarded as a rare orchid. Even up to the mid 1980's knowledgeable authors such as Barnham (1982) and Elliot and Jones (1984) were describing it as rare. Elliot and Jones (loc. cit.) even stating that only five plants had been discovered at that time.

The recognition that this hybrid was widespread but sporadic was a long time coming. Upton (1989) discussed the increasing frequency of its discovery but Jones (1988) still regarded it as "very rare". Certainly, it is not found at the same frequency as other natural hybrids such as D.X gracillimum and D.X delicatum. However, it would not be as scarce as some of the natural hybrids amongst the terete-leaved orchids of Dendrobium Section Rhizobium (see Wallace 1979 for a discussion on Sect. Rhizobium hybrids). I would venture that D.X suffusum would be the third most abundant natural hybrid in NSW behind D.X gracillimum and D.X delicatum.

As expected, the distribution of D.X suffusum corresponds with the majority of the overlapping range of the parent species.

The range of D.kingianum is given as from just north of the Hunter River in NSW (Upton 1989) to Carnarvon Gorge, west of Rockhampton Qld. (Clemesha 1965, Willersdorf 1968). D.gracilicaule is found over a far wider range, being recorded as occurring north from the Hawkesbury River NSW to the Bloomfield River in North Queensland (Dockrill 1969). Isolated plants of D.gracilicaule have been found south of the Hawkesbury River at Narrabeen (Upton pers. comm.), near Colo (pers. obs.) and apparently the Illawarra region (R.Tunstall pers. comm.).

The southerly distribution of D.X suffusum is so far the Lansdowne district in the Manning Valley (Gregory 1977, No.11). In the north, I was only able to confirm the existence of three plants from the Queensland portion of the overlap in distribution of the parents. The locations are Kilkoy near Somerset Dam, No.55, Christmas Creek on the Lamington Plateau, No.54 and the Numinbah Valley near Beechmont, No.40. Enquiries of its existence in the Toowoomba district, as reported by Upton (1989), failed to reveal any natural occurrences of this hybrid. There is hearsay evidence only of the collection of a plant many years ago on Tallabudgera Headland (Gifford pers. comm.) but this is unlikely due to the absence of the parents at this locale.

There are no real centres of distribution for D.X suffusum, with plants occurring throughout the expected range wherever the parents grow in proximity. Figure 1 records all localities known to me where D.X suffusum has been found.

There is no apparent altitudinal bias for its occurrence, having been collected from approximately 300' AMSL on North Brother, No.1, up to 2400' AMSL in the Lamington Plateau, No.54.

The parents of D.X suffusum have long been accepted as D.kingianum and D.gracilicaule. There is no reason to doubt this. Artificially propagated specimens of the same cross fall well within the range of vegetative and floral characteristics of the natural hybrids.

My investigations into the occurrence of D.X suffusum in the wild revealed an overwhelming predominance of plants having been found growing lithophytically. In fact, of 20 plants where the original collection data is known in this respect, only two were found on trees, Nos.45 & 54. The almost exclusive lithophytic habit of D.kingianum and the predominately epiphytic habits of D.gracilicaule led me to speculate, then experiment, on the reasons for this apparent bias.

Dr. Peter Adams (in litt. 8 Aug.1989) suggested that the difficulty of locating plants growing epiphytically, particularly out of flower, could contribute to the low numbers of reports of an epiphytic habit for D.X suffusum. This may well be the case but there may be other reasons for the bias.

I decided that, because a very high percentage of D.X suffusum grow on rocks, often amongst D.kingianum, it was not unreasonable to assume that D.kingianum was the pod parent. Admittedly, orchid seed can disperse some distance from the capsule but, even considering the sample size is small, the observed difference between lithophytic and epiphytic habit for D.X suffusum is significant.

I experimented to prove this theory in September 1988. I pollinated 10 flowers of D.kingianum with pollen from five different D.gracilicaule and did the reverse pollination on 10 flowers of D.gracilicaule.

Although no doubt crudely performed, I attempted as far as possible to replicate the actions of a bee as an agent of pollination. I was familiar with the method having recently observed a Honey Bee Apis mellifera pollinate D.kingianum (Smedley 1989).

The natural pollinators of D.kingianum are small native bees of the genus Trigona (Adams and Lawson 1988). In view of the number of natural D.X suffusum extant, certain species of Trigona bees probably play an as yet undetermined role in the pollination of D.gracilicaule.

The flowers of D.gracilicaule are generally much smaller than those of D.kingianum and the aperture between the rostellum and the side lobes of the labellum is correspondingly small. I would suggest that it would be very difficult for a Trigona bee carrying D.kingianum pollen on its thorax to successfully negotiate this orifice and deposit its load of pollen in the correct place.

Parallels can be drawn between this statement and the difficulties of pollinating smaller plants of D.kingianum. Although referring to A.mellifera, I have discussed these difficulties elsewhere (Smedley, 1989).

Another significant fact to emerge from this experiment was the difficulty in placing the D.kingianum pollen within the stigmatic cavity of D.gracilicaule. This was due to the D.kingianum pollen, from all plants used, being at least twice the size of the D.gracilicaule pollen. D.kingianum pollen is approximately 1.2 to 1.5mm in length and that of D.gracilicaule about 0.7mm.

Even with the D.kingianum pollen successfully adhering to the D.gracilicaule stigmatic surface, the growth of a mature capsule and the liberation of seed occurred in only one of the 10 pollinated flowers. Observations after pollination indicated that this failure to form capsules could be attributed to the failure to successfully secure the D.kingianum pollen onto the stigmatic surface of the D.gracilicaule. The pollen mass was simply too large and was pushed out and away from the stigmatic cavity by the swelling of the column. The pollen grains could not then germinate and there could be no fertilisation.

Most plants of this hybrid are self infertile (Adams 1988) thereby limiting the build up of this taxon in a natural ecosystem. Clemesha (in litt. 5 Oct.1988) reports similar results for D.X delicatum; over 75% of plants he tested were self infertile.

The procedures followed above may not pass a rigorous test of genuine scientific research. The results do however, give credence to my contention that D.kingianum is most likely to be, if not always so, the pod parent in the creation of natural D.X suffusum.

Pseudobulbs range in height from 8cm for a clone from Glen Iffer, No.30, to 50cm for a plant from the Hastings Valley, No.51. The majority grow to around 20-25cm.

All pseudobulbs are basically slender and fusiforme, following the shape of the D.gracilicaule parent. There are generally up to four leaves per pseudobulb but there can be up to six, No.51.

The regular production of aerials is uncommon, being only recorded from plants from Dorrigo, No.58, The Pinnacle, No.07 and Nymboida, No.53. Most plants would probably be induced to produce aerials if under stress or damaged.

There is as much range and variation in the size and colour of the flowers of D.X suffusum as there is in its parents. In fact, D.kingianum is probably the most variable Australian epiphytic orchid in respect of flower size and colour; from 10mm or less to greater than 30mm in width and from crystalline white in all its parts through the many shades of pink to the deepest burgundy.

The flowers of D.gracilicaule are also variable but to a far lesser extent. The variations are mainly in the degree of light purple present (mostly absent) in the labellum and the extent of the red/brown spotting on the reverse of the petals and sepals. The base colour of the segments can vary from a light yellow to deep gold.

It is not surprising then, that the results of hybridisation between these two species produce much variation in the colour, size and shape of the flowers in the progeny.

Size of flowers ranges from a meagre 9mm to more than 20mm in the case of those that more closely resemble D.kingianum. The number of flowers per raceme can be up to 14.

The extremes of flower colour within D.X suffusum are alba plants, such as from Dorrigo, No.53, to the exceptional clone from Cairncross State Forest, No.24, with rich burnt orange/gold flowers with heavy burgundy spotting on the reverse and a well marked purplish labellum. The photographs accompanying this article show some of the variations to be encountered within natural plants.

The majority of plants have light pink flowers with varying degrees of darker pink markings on the reverse. A smaller number of specimens are shades of green on the face of the segments. Some attractive plants have well marked labellums, particularly from the Border Ranges area. These plants are no doubt influenced by the bright purple labellums of D.kingianum var.silkockii common in the area.

I agree with Gregory (1977) that most plants of D.X suffusum resemble the D.gracilicaule parent in flower shape. There are some, such as the Cairncross State Forest plant, No.24 and the one from the Hastings Valley, No.51 that resemble D.kingianum. It is these that are the most horticulturally desirable, not that D.X suffusum has ever been a "fashionable" orchid.

Many people assisted with this project and it is difficult to acknowledge all individuals who have helped with information. Nevertheless, I am particularly grateful for the assistance of Ted Gregory of Mount Tambourine Qld., David Banks of Northmead NSW and David Mitten of Maitland NSW for much information and pieces of plants in their possession. Similarly, John Roberts of Lower Beechmont Qld. helped with information on plants that he and Danny Ross have found in Queensland. Dr Peter Adams of Mount Evelyn Vic. criticised an early re-write of the paper, provided me with his reference concerning the reproductive biology of D.X suffusum and gave me data on plants of which I was not aware.

Finally, I must thank Steve Clemesha of Woolgoolga NSW and Charlie Fourro of North Curl Curl NSW who were the only growers to respond to my plea for information in The Orchadian.

This paper, in an earlier version, was prepared originally for submission to the ANOS Judging Panel in 1990 to satisfy a criterion for qualification as an ANOS Certificated Judge.

Adams P.B. 1988, The spectrum of fertility in Australian Orchid Species. In: Reproductive Biology of Species Orchids. Edit. P.B.Adams. School of Botany and Orchid Species Society of Victoria, pp 25-35.

Adams P.B. and S.D.Lawson 1988, Multiple Bee Pollinators of Dendrobium kingianum Bidw. in the Natural Habitat. The Orchadian Vol.9 pp103-107.

Barnham D. 1982, The Basics of Native Orchid Growing -3. The Orchadian Vol.7 p89.

Barton L. 1981, Some Orchids of the Hastings Valley. The Orchadian Vol.7 p30.

Betts J.J. 1984, Obituary - The late Len Archer. The Orchadian Vol.7 p250.

Cady L. 1964, A New Species of Dendrobium for NSW Dendrobium suffusum sp.nov. The Orchadian Vol.1 pp80-81

Clemesha S.C. 1965, Dendrobium kingianum Bidw. from North to South. The Orchadian Vol.2 pp34-36.

Corrigan M. 1987, Recent Recordings in the Coffs Harbour-Dorrigo-Grafton Triangle. The Orchadian Vol.8 pp236-237.

Dockrill A.W. 1969, Australian Indigenous Orchids Vol.1. Society For Growing Australian Plants, Sydney.

Elliot W.R. and D.L.Jones 1984, Encyclopaedia of Australian Plants Suitable for Cultivation Vol.3 p235. Lothian Publishing Company Pty Ltd. Melbourne

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Smedley D.I. 1988, Request for Information, Readers Forum. The Orchadian Vol.9 p84.

Smedley D.I. 1989, Notes on the Pollination of Dendrobium kingianum. The Orchadian Vol.9 pp177-178.

Upton W.T. 1989, Dendrobium Orchids in Australia. Houghton Mifflin Australia, Melbourne.

Upton W.T. & Clemesha S. 1967, in Kirkland K., 'Australian Orchids' - Proceedings of the Fifth World Orchid Conference. Orchid Society of NSW Ltd.

Wallace B. 1979, Introgression Among Australian Fleshy-leaved Dendrobiums. The Orchadian Vol.6 pp.58-59.

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POSTSCRIPT

Since this article was completed I have been informed of the discovery of a number of other clones of D.X suffusum, predominantly in the Tenterfield area of NSW. I would continue to welcome information on any other D.X suffusum encountered in the wild. I can be contacted by e-mail or at the address at our Contact Us page. Darryl Smedley.

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