Pleurothallidinae (Orchidaceae)

Abstract

A number of orchids belonging to Masdevallia and some closely allied genera are described from a horticultural perspective. Botanical information is included where available.

Keywords: Orchidaceae, Pleurothallidinae, Dracula, Dryadella, Masdevallia, Restrepia

Introduction

Orchids of the subtribe Pleurothallidinae are among the most popular of the "species" orchids – naturally occurring species of plants, rather than the (usually) more showy hybrids – grown by amateurs. Four genera, Dracula, Dryadella, Masdevallia and Restrepia, are particularly often seen in collections.

Systematics

Pleurothallid systematics are not in an entirely satisfactory state: some recent genetic research (e.g. Pridgeon et al. 2001) suggests that several genera, as presently defined, are paraphyletic. For example, a cladogram - available on Lou Jost's web site - shows a paraphyletic Dracula split by Porroglossum.

Kingdom Plantae

Phylum (Division) Spermatophyta

Class Liliopsida

Order Orchidales

Family Orchidaceae

Subfamily Epidendroideae Lindley

Plants epiphytic or terrestrial; some parasitic. Leaves spirally arranged or distichous. Anthers single; terminal, incumbent (bent downward during development) so as to form a right angle with the column axis or pointed backward in many genera. Pollinia with or without caudicle and viscidium; soft and mealy or hard; (2, 4, 6, or 8 (12)). Pollen in tetrads. Stigma entire or 3-lobed; sometimes with viscidium. Rostellum. Ovary uniloculate. Seed coat transparent.

Tribe Epidendreae Dressler

New world and old world representatives, comprising nine or ten subtribes:

• Adrorhizinae: 2 genera, tropical Asia (India, Ceylon)
• Glomerinae: 7 genera, tropical Asia and Australasia
• Polystachyinae: 4 genera, pantropical but primarily Africa

New World:

• Arpophyllinae: 1 genus
• Coeliinae: 1 genus
• Laeliinae: ~43 genera
• Meiracylliinae: 1 genus
• Pleurothallidinae: ~28 genera
• Sobraliinae

Subtribe Pleurothallidinae Lindley 1830

Type Genus: Pleurothallis R. Brown 1813

Description: Ramicauls non-pseudobulbous, single-leaved. Ovary articulated; deciduous from the pedicel.

Discussion: In Dressler's (1981) classification of the Orchiaceae, the Pleurothallidinae is the one of ten subtribes of the Epidendreae having the greatest number of species – approaching 4000 species in approximately 30 genera, including:

Acianthera - ?Pridgeon, Solorzano & Chase 2001
Acostaea Schlechter 1923
Anathallis - ?Pridgeon, Solorzano & Chase 2001
Anthereon - ?Pridgeon, Solorzano & Chase 2001
Barbosella Schlechter 1918
Barbrodria Luer 1981
Brachionidium Lindley 1859
Chamelophyton Garay 1974
Condylago Luer 1982
Draconanthes Luer 1996
Dracula Luer 1978b (see below)
Dreslerella Luer 1976
Dryadella 1978b (see below)
Echinosepala Pridgeon & Chase 2002
Frondaria Luer 1986
Jostia Luer 2000
Lepanthes Swartz 1799
Lepanthopsis (Cogniaux 1896) Ames 1933
Luerella Braas 1979 (may be subgen. of Masdevallia)
Masdevallia Ruíz & Pavón 1794 (see below)
Myoxanthus Poeppig & Endlicher 1836
Octomeria R. Brown 1813
Ophidion Luer 1982
Phloeophila ?author
Platystele Schlechter 1910
Pleurothallis R. Brown 1813
Pleurothallopsis Porto & Brade 1937
Porroglossum Schlecter 1920
Restrepia Kunth 1816 (see below)
Restrepiella Garay & Dunsterv. 1966
Restrepiopsis Luer 1978b
Salpistele Dressler 1979
Scaphosepalum Pfitzer 1888
Specklinia Lindley 1830
Stelis Swartz 1799
Teagueia Luer 1986 (may be subgen. of Masdevallia)
Trichosalpinx Luer 1983
Trisetella Luer 1980
Zootrophion Luer 1982

A selection of the most commonly cultivated genera is further described below.

Genus Dracula Luer 1978b, p. 190

Type Species: Dracula chimaera (Rchb.f. 1872, p. 463) Luer 1978b, p. 194

Habit: Epiphytic and terrestrial.

Description: Plants perennial; small to large; caespitose to shortly repent or ascending. Leaves comparatively thin, sometimes plicate, with a sharply defined midrib; glabrous; light to dark green; linear to elliptical; notched with a mucro in the sinus. Ramicauls ascending to erect; non-pseudobulbous; shorter than the leaf; unifoliate; partially or completely enclosed by tubular sheaths. Racemes commonly pendant; arising from the ramicaul with an annulus a considerable distance below the abcission layer. Flowers borne singly or successively. Sepals long tailed. Petals characteristically small, thickened apically, usually verrucose between a pair of valvelike laminae; flanking the column. Lip clearly divided into a cleft hypochile and a more or less rounded, concave epichile; epichile often coursed by lamellate, radiating "veins." The concave base is hinged to the stout column-foot, but in a few species the attachment becomes immobile with adnation of the base to the column-foot. Column well developed, semiterete, with a hooded ventral anther and stigma, and a short thick foot. Two pollinia.

(After Luer 1993.)

Distribution: Over 80 species are known from Central America and the northwestern Andes.

(Read more.)

Genus Dryadella Luer 1978b, p. 207

Type Species: Dryadella elata (Luer 1978a, p. 199) Luer 1978b, p. 206

Habit: Epiphytic.

Description: Plants perennial; small to very small (3 to 6 cm.); densely tufted, growing into large clumps from creeping rhizomes. Leaves single, erect, with short ramicauls; narrow, fleshy. Flowers small, produced singly or successively in short racemes from an annulus. Sepals commonly caudate, connate basally into a gaping cup. Where the lateral sepals are deflexed from the cup above the base, a transverse callus like a transverse fold extends across the width of the sepals so that the petals and lip above protrude over the characteristic "dam." Petals short, broad and multi-angled. Lip unguicalate; the bicallous blade of the lip is hinged to the column foot by a long slender claw. Column broadly winged and hooded with a ventral anther and stigma. There are two 2 pollina.

(After Luer 1986a.)

Distribution: Approximately 40 species; distributed from southern Mexico to southern Brazil and northern Argentina.

(Read more.)

Genus Masdevallia Ruíz & Pavón 1794

Type Species: Masdevallia uniflora Ruíz & Pavón 1798, Syst. Veg. 238

Habit: Epiphytic, lithophytic to terrestrial.

Description: Plants perennial; very small to large; weak to robust; the rhizome very short to elongate between ramicauls; ascending to erect, rarely descending. Leaves coriaceous. Ramicauls short; ascending to erect, rarely descending; non-pseudobulbous; shorter than the leaf; unifoliate; partially or completely enclosed by 2 or 3 thin, imbricating tubular sheaths near the base. Racemes arising from the ramicaul with an annulus a considerable distance below the abcission layer. Flowers single, successive, or simultaneous, few to many. Sepals variously connate; commonly tailed. Petals small, with a callous margin often developed into a tooth. Lip more or less lingulate, hinged to an incurved extension from the apex of the column-foot. Column terete, with a hooded ventral anther bearing two pollinia.

(After Luer 1986b.)

Distribution: About 350 species are widely distributed from Mexico to southern Brazil.

(Read more.)

Genus Restrepia Kunth 1816

Type Species: Restrepia antennifera Kunth 1816, Nov. Gen. Sp. Pl. 1: 367

Habit: Epiphytic to terrestrial.

Description: Ramicauls clothed by a series of inflated, compressed, more or less imbricating sheaths. Flowers solitary. Dorsal sepal and petals clavate; synsepal colourful. Lip with concave hypochile flanked by a pair of hair-like appendages, and fixed to the pedestal-like column-foot by a short, rigid rod. Four pollinia.

(After Luer 1986a.)

Distribution: About 80 epithets have been published, but many are synonyms leaving perhaps 25 fairly well-defined species with a distribution centred upon the high Andes of Colombia and Equador.

Conservation

Many species of this group are limited in their geographic distribution (e.g. Dracula psyche, D. robledorum) and highly exposed to even minor environmental disturbance.

The continuing destruction of the world's rainforests, with the consequent loss of delicate habitats leading to the extinction of whole species, is well documented. What is less clear is whether local and international efforts, intended to protect endangered species, sometimes contribute to the problem by preventing the collection of endangered taxa from doomed areas. One occasionally hears of ridiculous cases, possibly untrue, where collectors are prevented from saving the epiphytes from already felled timber because the plants are "protected."

It is also possible that a number of orchid species have become extinct in their native habitat in recent years, and exist now only in collections. There they may be safe for a while, provided they are not lost to disease or hybridised out of recognition (orchid growers have long had a penchant for trying to "improve" upon nature). One day, if we are very lucky, we may see their introduction back into some protected wild place.

Reluctant as we may be to admit it, our best chance to ensure the preservation of rare orchids presently lies in their widespread cultivation by enthusiasts. When there is a Dracula psyche growing in every living room, then the plant will be safe.

Hybrids

Hybrids are not described in any detail on this site. Some, especially those with names which might be misconstrued as applying to a legitimate natural species such as Masdevallia Heathii, may be listed for reference purposes only.

Beginning a Collection

Most people beginning a collection of these plants want to start immediately with the "glamour" species: Dracula erythrochaete, D. vampira, Masdevallia coccinia, M. veitchiana, and so on. These are undeniably beautiful plants and nearly all enthusiastic growers will acquire them at some time or another. However, they are not necessarily the best plants to begin with. To illustrate the point, D. erythrochaete and D. vampira both produce inflorescences (flower stems) which grow down through the potting mix and appear through holes in the bottom of the pot. This fact alone presents considerable difficulties to someone hoping to simply grow a few plants on a shelf in their home. For someone interested in the genus, there are a number of erect-stemmed Dracula, any one of which could be a better first choice.

The choice of species obviously depends very largely on what the grower hopes to gain from the experience of owning them. An ardent conservationist, for example, may wish to collect endangered species for propagation. Another may just want an attractive and unusual pot-plant, in which case M. veitchiana may well be the correct first choice. Those wishing to show their plants in competition, will undoubtedly prefer named clones to plants without a pedigree.

However, those motivated mostly by curiosity or a desire to learn more about the plants will probably derive the most satisfaction from a selection of species chosen to exhibit a variety of morphological characteristics. Masdevallia infracta, for example, is a readily available species with single flowers growing from a fleshy green triquetrous inflorescence which persists from season to season, two small glandular swellings on the lateral petals just inside the flower cup, and an easily visible, fixed lip. Contrast this with M. melanopus, another common species, characterised by multiple flowers on a thin inflorescence which flowers only once.

Miniatures – plants which remain small, even when fully developed – offer other advantages, especially to those with limited space. Masdevalia pteroglossa is a superb example; not only is the plant extremely small but the flowers are exquisite and plentiful. Any of the Dryadella species will also qualify, though in my experience they can sometimes be quite difficult to keep.

Culture

Some Pleurothallids are difficult to grow. Some, in fact, have defied cultivation. Fortunately, many others are easy to grow, and new species are appearing year after year in commercial growers’ catalogues.

As we have noted, most species are epiphytes from the cloud forests of Central and South America, frequently from high altitudes in the Andes. It is easy to guess that, in general, they will require cool to intermediate temperatures, continual moistness, regular light feeding, and shade to semi-shade.

Temperature

A winter minimum of 10^oC is usually recommended for the group as a whole. However, it must be remembered that Masdevallia and allied species come from a wide geographical range and a variety of altitudes. Some species require more tropical conditions.

Cool-growing plants are often susceptible to losing buds in warm weather or if taken indoors. Some preferring more warmth may promptly lose most of their leaves, or outright die, after experiencing a cold snap. I have found several Dryadella to behave like this.

Potting

It is often said of orchids in general that they should be under-potted, i.e. that they should be kept in pots which are only just large enough to accommodate the plant. The writer has never found this to be necessary to the well-being of the plant: healthy specimens appear to grow strongly in any sized pot. However, some species do seem to flower more regularly when crowded, although it is difficult to imagine any physiological reason why this may be so.

Another piece of conventional wisdom is to re-pot as infrequently as possible. In general, this is good advice. However, upon first taking delivery of a new plant, any detrimental effect of disturbing the root system is outweighed by the great advantage of having the plant in a standard potting mixture, the properties of which are known to the grower.

Substrate

The writer has always used a relatively fine-grained 100% bark potting medium sold as "Prime Orchid Mix" for Cymbidium plants.

Watering

Like most epiphytes, Pleurothallidinae plants are very sensitive to any build-up of mineral salts in the potting medium. Tray watering should be avoided. It is best to water from the top and allow the excess water to run freely from the holes in the bottom of the pots. Watering by immersing the pot in water seems to work well - indeed, some delicate plants such as the tiny Dryadella species seem to prefer this method - provided the pots are permitted to drain freely afterwards. Unfortunately this approach rapidly becomes impractical where one has many plants and limited time. It is probably a good idea to water from the top at least occasionally in any event.

Note that bark does not wet easily; when hand-watering, it is best to water once, wait a while for the bark to absorb the water, then water again.

Feeding

The watering regime adopted for orchids is designed to prevent a build-up of soluble salts in the substrate, which is reputed to quickly kill the plants. The writer has not been game to try proving this argument with his own collection, but assuming its validity for the present, the obvious conclusion is that orchids of all kinds prefer a low-salt environment around their roots.

In apparent contradiction, most orchids - including those described herein - do rather well with frequent light fertilizing. Incorporating a completely soluble fertilizer with watering is the usual recommendation. However, that is often difficult for the amateur grower.

Contrary to the usual recommendations for these or any orchids, I have achieved good results using a slow-release solid fertiliser (Osmocote). It may not work for everyone, and presumeably there is good reason why this approach is widely deprecated, but it works for me.

Humidity

Orchids in general prefer high humidity. One of the most obvious symptoms of humidity which is too low is that the sheaths around new leaves stiffen, preventing the leaves from breaking through easily. The leaves continue to grow inside the unruptured sheath and become crumpled back upon themselves. When they finally do break out, the leaf is usually left with a characteristically wrinkled appearance.

Generally species with thin delicate leaves such as Dracula vampira or Masdvallia calocodon are most susceptible because the stronger, thicker leaves of a plant such as M. civilis will easily force their way through the thin sheath. However, even some robust-leaved species such as M. veitchiana or M. melanopus suffer somewhat.

The solution is to maintain a high level of humidity. However, while this may be simple in a dedicated shade house (mine has an earth floor which is kept moist) it is very difficult to attain with a few plants grown indoors.

(Further cultural information.)

Hygiene

In fact, Masdevallia species are rather resistent to pests and diseases. When plants are not receiveing the correct culture, the usual symptom is simply a lack of vigour; old leaves die off more rapidly than new ones grow, and eventually this attrition reduces the plant to nothing.

Problems can be mimimised, or at least prevented from spreading, by ensuring that plants leaves do not touch one another, and that pots and any tools are thoroughly cleaned before reuse.

Scale

Scale is one problem I have encountered. Scale is a coccid insect (order Homoptera, sometimes considered to be a suborder of the Hemiptera, superfamily Coccoidea) with a hardened resinous scale covering the female, which is more or less permanently anchored to the plant by its mouthparts. Males are winged and non-feeding. Juveniles resemble the females. They are related to mealy bugs.

Scale can difficult and at times almost ineradicable. Plants with scale should be separated from healthy plants if they cannot be cured quickly. Generally, persistent spraying with Summer Oil (e.g. Yates Conqueror Oil) will (eventually) do the trick.

Snails

Snails are another manace, capable of decimating a whole season's growth overnight. In an outdoor shade house, use snail baits on the ground, on the shelves, and frequently inspect plants for these unwelcome visitors.

References

Cogniaux, A. 1896: Martius, Flora Brasiliensis 3(4): 319-646.

Dressler, R.L. 1981: The Orchids: Natural History and Classification. Harvard University Press, Cambridge.

Lindley, J. 1830: Genera and Species of Orchidaceous Plants, 1-45.

Luer, Carlyle A. 1978a. Phytologia 39.

Luer, Carlyle A. 1978b: Dracula, a New Genus in the Pleurothallidinae. Selbyana 2: 190-198.

Luer, Carlyle A. 1986a: Icones Pleurothallidinarum I – Systematics of the Pleurothallidinarum. Monographs in Systematic Botany from the Missouri Botanical Garden Vol. 15.

Luer, Carlyle A. 1986b: Icones Pleurothallidinarum II – Systematics of Masdevallia. Monographs in Systematic Botany from the Missouri Botanical Garden Vol. 16.

Luer, Carlyle A. 1993: Icones Pleurothallidinarum X - Systematics of Dracula. Monographs in Systematic Botany from the Missouri Botanical Garden Vol. 46.

Pridgeon; Solorzano & Chase 2001

Pridgeon & Chase 2002