Dendrophylax lindenii

Ghost Orchid
Conservation status
Endangered (IUCN 2.3)
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Monocots
Order:	Asparagales
Family:	Orchidaceae
Subfamily:	Epidendroideae
Tribe:	Vandeae
Subtribe:	Angraecinae
Genus:	Dendrophylax
Species:	D. lindenii
Binomial name
Dendrophylax lindenii (Lindl.) Benth. ex Rolfe

Dendrophylax lindenii, the Ghost Orchid - not to be confused with the Eurasian Ghost Orchid (Epipogium aphyllum) - is a perennial epiphyte from the orchid family (Orchidaceae). Other common names include Palm Polly and White Frog Orchid. Formerly classified under Polyrrhiza this orchid has recently been moved to the genus Dendrophylax.

Name

Synonyms include :

• Aeranthes lindenii (Lindl.) Rchb.f. in W.G.Walpers, Ann. Bot. Syst. 6: 902, 1864.
• Angraecum lindenii Lindl., Gard. Chron. 1846(1): 135, 1846.
• Polyrrhiza lindenii (Lindl.) Cogn., Symb. Antill. 6: 680, 1910.
• Polyradicion lindenii (Lindl.) Garay, J. Arnold Arbor. 50: 467 (1969). (This name is still used by many authors).

The database World Checklist of Monocotyledons of Kew Botanical Gardens at present considers Dendrophylax lindenii as the accepted name, while Polyrrhiza lindenii is considered as a homotypic synonym.

Its specific epithet "lindenii" is derived from its discoverer, the Belgian plant collector Jean Jules Linden who saw this orchid for the first time in Cuba in 1844. Much later it was also discovered in the Everglades in Florida.

Biology

Images courtesy of Mick Fournier

This orchid is a leafless epiphyte of the Vandeae family. The plants consist of large masses of photosynthetic roots, anchored as a network on trees. It is found in moist, swampy forests in southwestern Florida and Cuba, and other Caribbean islands.

This orchid is an exceptional monocot, as it consists of a greatly reduced stem and the leaves have been reduced to scales. The bulk of the plant consists only of flat, cord-like, green roots with distinctive "track marks". These white track marks are called pneumatodes and function in much the same manner as stomata allowing the photosynthetic roots to perform gas exchange to support photosynthesis. These roots are used for moisture absorption and their chloroplasts for photosynthesis. The outer layer, the velamen, takes care of acquiring the nutrients and the water uptake. It also protects the inner layers.

This orchid is a distant relative of the African and Indian Ocean genus Angraecum; it seems that orchid seed, blowing like dust, crossed the Atlantic at least once and successfully colonized new habitat. Most leafless neotropical orchids in the Angraceum family are opportunistic epiparasites and harness mychorrzial fungi which have been documented to harm host trees by obtaining nourishment from their hosts through their mychorrizial symbiots. This species shows similar specialization and has a decided preference for specific host trees. Vascular studies of leafless orchids in the Vandeae has determined that the loss of leaves evolved in conjunction with indirect parasitism of host trees.

This is an endangered orchid in the wild. Cultivation outside of its native environment has proven exceptionally difficult, but not impossible. Although many fail in the attempt to raise seedlings grown in sterile culture into adult plants, some have succeeded. This orchid is listed on the Appendix II of CITES and is fully protected by Florida state laws and should not be removed from the wild. Since wild plants form mutualistic relationships with mycorhizzial fungi and their host tree, plants taken from the wild typically have become dependent on their mycorhizzial symbiots and are not equipped to survive once removed from their hosts. Wild collected plants typically do not survive removal from their habitat, and die within a year. Plants in habitat are typically found growing on the central trunk or large main branches of living trees. The Ghost Orchid seems to prefer Annona glabra (Pond-apple) trees, or on occasion Fraxinus caroliniana (Pop Ash) trees, being from eye-level to only a few feet above eye-level.

This orchid blossoms between June and August, with one to ten fragrant flowers that open one at a time. The white flower is 3–4 cm wide and 7–9 cm long and is borne on spikes arising from the root network. During its peak fragrance emittance in the early morning, the scent is fruity, resembling an apple. The lower petal produces two long tendrils that twist slightly downward, resembling the back legs of a jumping frog. Its bracts are scarious - that is, thin, dry, membranous, and paperlike. Since the roots of this orchid blend so well with the tree, the flower often seems to be floating in midair, hence its name of "Ghost Orchid".

Pollination is done by the giant sphinx moth, the only local insect with a long enough proboscis to pollinate the flowers and access the extremely long nectar spur. In this regard it may be said to be the America's answer to the Madagascar orchid Angraecum sesquipedale, which led Charles Darwin to predict that a long-tongued species of moth would be found to fertilize it. Years later the moth responsible was discovered: Morgan's hawk moth Xanthopan morgani. The larvae of the giant sphinx moth feed on Annona glabra (Pond Apple), the same trees Ghost Orchids are typically associated with and used as hosts.

The leafless habit seen in this species is actually quite common among all epiphytic orchids during their early life cycle. Most epiphytic orchids and virtually all terrestrial species of orchids upon germination form a mycorhizzial association with fungi in the order Rhizoctonia and enter a definite saprophytic stage. During this stage the plant simply forms into a mass of cells and produces a protocorm which in many species grows through decomposing humus and produces ephemeral leaves on a burrowing highly reduced stem. Many orchid species never leave this stage and continue as saprophytes, notably, Orchids in the family Gastrodia, as well as Epipogium aphyllum, the Eurasian Ghost Orchid, which is also an endangered species. Orchids from sunny, wet forest environments typically develop leaves and photosynthesis rapidly, while some epiphytic species, such as Stanhopea and Catasetum, have a prolonged saprophytic stage in decomposing wood before developing leaves and photosynthesis. Dendrophylax species retain the early stage characteristics of a highly reduced stem and ephemeral leaves while initiating photosynthesis in its roots and retains many features of a saprophyte, although the plants are technically opportunistic epiparasites. The actual mechanism of reduced leaves involves production of leaf meristem in which the stomata are essentially 'stuck' open, which results in the leaf meristem dehising rapidly as it is forming, resulting in a leaf scale, a saprophytic adaptation.

Cultivation

Plants can be successfully grown in a terrarium-like environment mounted bare root on a decay resistant, untreated wood stock in which the wood is laid horizontally on top of a bed of living spangum moss, as the plants require high humidity and stagnant air, or in a wardian case or greenhouse which approximates these conditions. Plants should not be allowed to cross pollinate and set seed unless the plant is very large, at least 10 inches across, as plants without sufficient biomass will transfer all of their stored reserves into making a very large seed pod and the plants behave much like an annual and die after seed set. Plants in cultivation do not typically have their host tree and mycorrizzial symbiots to draw reserves from and only very large plants have sufficient reserves to make the very large seed pods (up to 14 inches in length) without killing the plants. These plants should be given 1/4 strength fertilizer in distilled or other low salt water sources weekly.

The plants are intolerant of water with high levels of dissolved salts and will result in the roots dying off from the tips. Continued exposure to chlorinated tap water will usually kill these plants, with the tips of the roots yellowing and rapidly dying back to the reduced stem. It is normal for the plants to periodically consume and dehise older roots, but this process does not yellow the roots, they simply shrivel and turn gray then dehise completely. Healthy plants will exhibit vigorous lime green root tips which are in an active state of growth. The plants root tips will grow continuously provided they receive bright light and regular fertilization and watering, with only a short resting period in late fall/early winter. Water should never be allowed to remain standing in the roots nor should any portion of the plants roots to be immersed in standing water for any significant period of time.

Plants in cultivation typically have a very different appearance from plants in habitat, and are far less robust. Plants in habitat exhibit thick cord-like roots which tightly hug and encircle their host tree with two distinct layers, the side facing the light is green and the layer attached to the tree resembles the root structure of saprophytic orchids such as Neottania and is typically heavily infected with mycorhizzial fungi. Plants in cultivation without their mycorhizzial symbiots have very slender roots and will form semi-shperical "root balls" with large numbers of roots growing vertically away from the central root mass much like leaves to increase surface area for photosynthesis. The roots of these plants will also tend to produce new plantlets in a starfish like manner from broken or damaged roots or from roots which have grown longer than 12 inches, a growth habit shared with other members of the genus Dendrophylax.

Although plants in habitat occasionally experience light frost with some root tip damage, as a rule, the plants should not be subjected to freezing temperatures. Freezing temperatures except for very short periods will kill these plants in cultivation. Blooming is triggered by subjecting the plants to a cool, dry resting period with only very light misting every few weeks and lowering the humidity in the growing environment for a period of several months in late fall and early winter when the plants are large enough to support flowering, typically with a root mass of 7-8 inches across.

Newly forming flowers will appear from the highly reduced stem from the center of the root mass and are difficult to distinguish from aerial roots until the flower starts to develop. When new growth is apparent after giving the plants a resting period, resume normal watering. Plants which are large and have set seed pods should be given more frequent fertilizing and should limit only a single seed pod per plant by removing all but one seed pod from a plant. When attempting to produce seed pods from one of these plants, if the plant has multiple flowers all of them should be hand pollinated with pollenaria from a different plant if available, and only one seed pod allowed to remain on each plant, since not all of the flowers may successfully take. The pod resembles a very large vanilla bean (10 to 14 inches) and when mature contains hundreds of thousands of microscopic dust-like seeds. If seeds are to be used for sterile flasking, the pods must be harvested shortly before they open as the seeds must be removed from the mature pod and flasked under sterile conditions.

In habitat, successful pollination of this species appears to be an infrequent, but not rare, event. The plants also flower irregularly in habitat, and some years do not flower at all.

In popular culture

The plant plays a pivotal role in the non-fiction book The Orchid Thief, and the movie based on the book, Adaptation. The ghost orchid of Blair Audubon Corkscrew Swamp Sanctuary also inspired the fiction novel, Ghost Orchid.

External links

• Ghost Orchid (Dendrophylax lindenii) Information Page at The Florida's Native and Naturalized Orchids Website.
• GhostOrchid.info
• "Rare ghost orchid found in Fla. preserve" (AP, July 11, 2007)
• Corkscrew Swamp Sanctuary Ghost Orchid Page
• "A Ghostly Success In the Most Unlikely Place-Hale Method" [1]