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Vol. 13(1), pp. 10-16The McAllen International Orchid Society JournalJanuary 2012

A Detailed Review of Zelenkoa onusta (2001)

Wilma J. Ferry

Zelenkoa onusta (Lindley) M.W. Chase & N.H. Williams Lindleyana 16(2): 139 (2001).
Synonyms: Oncidium onustum Lindley, Gen. & Sp. Orch. Pl. 203 1833.
Oncidium holochrysum Rchb. f., Ham. Gartenz. 18: 33. 1862.

This species was originally classified as an Oncidium onustum by Lindley in 1833, but in 2001, Williams et. al., conducted DNA studies and reassigned it to a new genus. They determined it differs vegetatively and florally from all other Oncidiinae and is sister to a clade composed of many genera. Although it looks, at a glance, like a typical Oncidium, it does not have a column tabula infrastigmatica (a slab or enlarged column base under the receptive tip where pollen germinates), and was atypical in its habit. Finding it impossible to transfer this species to any other genus and maintain monophyly of such a taxon (a group of organisms having a common descent from a single ancestor), they erected a new genus. The name Zelenkoa was selected to honor Harry Zelenko, an American artist and the illustrator of The Pictorial Encyclopedia of Oncidium (Zelenko, 1997). On a personal note, the illustration by Zelenko of this plant is magnificently life-like.

Fig. 1. Zelenkoa onusta (Ldl.) Chase & Williams. 2001. Photo: DSC_4393; Sun-20Nov11.

This species is found as an epiphyte, in the dry humid coastal lowlands of southwestern Ecuador and northwestern Peru, in areas where rainfall is scant, growing on various desert type plants and cacti. Baker (2006) states this species grows on cacti and trees in dry forests, usually near sea level, but collections from as high as 3950 ft. (1200m.) have been reported by Dodson (1980). Schweinfurth (1961) states plants are also lithophytic, growing on crevices of cliffs. Dodson & Bennett (1989) have found them on Palo Santo host trees (Bursera graveolens), on Charan (Caesalpinia corymbosa) and on Angolo (Pithecolobium multiflorum) in Peru blooming in late May through July or the southern hemisphere's early autumn to midwinter. In cultivation in the northern hemisphere it blooms from September to December (Fig. 1).

Fig. 2. Zelenkoa onusta. Close-in photo of plantlet. Photo: DSC_4409; Tues-29Nov11.

Fig. 3. Inflorescence arising from pseudobulb. Photo: DSC_4410; Tues-29Nov11

Zelenkoa onusta is diminutive in size, about 13 cm in height and tends to form clumps as its pseudobulbs grow closely spaced along a creeping rhizome. These pseudobulbs are egg-shaped with longitudinal ridges and furrows that appear to have dark spots. They usually have a single leathery leaf carried at the apex but can have two. The leaf is sharply pointed at the tip and conduplicate or folded longitudinally at the base. A thin line or groove is visible down the middle on the adaxil (upper) side and on the abaxial (lower) side, a ridge or keel is more pronounced on an older, drier leaf. The margins or edges are finely serrated. Each pseudobulb has 2-3 sheathing bracts and a well developed leaf-like sheath at its base. On a very juvenile pseudobulb two such leaf-like sheaths have been observed (Fig. 2), and it is from the longitudinal fold of a similar leaf-like sheath at the base of the pseudobulb that the inflorescence emerges (Fig. 3). The inflorescence is about 8-10 inches long with 8-14 yellow flowers held on the raceme. The flowers are yellow and about 2 cm (ca. 0.8 inches) horizontally by about 2.5 cm (1 inch) vertically. The small sepals are sharply pointed and triangular in shape with a reddish central line on their dorsal side. The petals and sepals are free (not united). The upper two petals are round with a midline indention and a terminal point. The 3-lobed lip is spread widely with the side lobes narrow compared with the rounded, distally deeply clefted midlobe. A basal callus is fused to the column. The labellum callus consists of a raised, concave shelf with a pair of projecting teeth. The column is short with a pair of crescent wings which form a hood over the anther. Each flower produces 2 hard, waxy pollinia. The ovary in cross-section is triangular. Its chromosome count is reported as 2n = 56. One pollinator, Xylocopa bee, has been reported.

Fig. 4. Inflorescence arising from pseudobulb. Photo: DSC_3760; Tues-30Sept10.

These small plants (Pl#030102-107 & Pl#110408-2) are growing happily on a shard of tree fern and a stick of wood in our greenhouse (Fig. 4). One was purchased from a vendor ten years ago and the other obtained about four years ago. In its habitat, the blooming season is from autumn to midwinter. In the greenhouse, it blooms in November with a single raceme of 14 small yellow flowers. Its size makes it ideal for growing in limited space, but could be mounted on tree fern or cork just as well. With such growing media, it requires high humidity. In its natural habitat the rainfall is light during the year, but generally additional moisture is received through dew and late night mist or fog, so in the greenhouse, they are misted nearly every morning, and spray-fertilized frequently (at times, even dipped-fertilized). However, more frequent mistings are done during the summer to avoid these plants being completely dry for any length of time.

Zelenkoa onusta and The Language of Botany

To find the most descriptive word that paints a picture of a thousand words, we sigh in frustration! We need that one word that can so eloquently and precisely convey to others the meaning of what is seen with our eyes. Botanical language employs just such vocabulary, and to dissect and understand that word, it may be beneficial to have a special dictionary. So with a botany dictionary in hand, we will compare the visual image of a flower with its universally accepted descriptive terminology. As we read a botanical description of an orchid, that handy dictionary will enable us to be more proficient in transliterating what is written about that particular orchid plant. As our vocabulary grows and expands, it becomes possible to see more with our mind's eye, with or without the actual plant in front of us. As well, perhaps we'll begin to look more critically at each of the living plants in orchid collections.

Let's explore our skill with what is written about Zelenkoa onusta. The following paragraphs present its botanical description, as published in Lindleyana 2001: 16(2). The bold print represents the parts of the plant with the vocabulary of the authors. These underlined words or terms are followed by the transliterations in parentheses.

Small, perennial, caespitose (growing in tufts or small dense clumps) herbs, epiphytic (growing on a plant), often on cacti, or lithophytic (growing on rock), with pseudobulbs (thickened or bulb shaped stems), clustered on a short rhizome (a surface or underground, more or less horizontal, stem).

Pseudobulbs ovoid (egg or pear-shaped), round in cross-section, ridged longitudinally, unifoliate (one-leafed), composed of a single internode, lower portions concealed by 2-3 sheathing bracts, the uppermost 1-2 with a lamina (a leaf-like sheathing) at its base.

Fig. 5. Sheathing arising from ridged side of pseudobulb. Photo: DSC_4411; Tues-29Nov11.

Leaves elliptic-lanceolate (narrow sword-like), coriaceous (thick and leathery), glabrous (not hairy), conduplicate (longitudinally folded), margins entire terminally (edges smooth at tip), but often serrate (saw-toothed) near the middle and base, eventually deciduous (losing their leaves) (Fig. 5).

Fig. 6. Infloresence arising basally from psb. Photo: DSC_4412; Tues-29Nov11.

Inflorescences produced laterally from a node at the base of the pseudobulb (Fig. 6), subtended (occurring immediately below) by a sheathing bract, much longer than the leaves, racemose (unbranched), many-flowered.

Flowers medium-sized, resupinate (twisting 180 degrees); pedicellate (the single flower's stalk), ovary glabrous (not hairy), twisted to orient the flowers.

Sepals free (not united), equal in size, much smaller than the petals, shortly elliptic, dorsally carinate (keeled or creased) and shortly acuminate (pointed).

Petals free (not united), much larger than the sepals, nearly orbicular (circular) with an apical cleft (indented at the end or point); lip broadly attached to the column (structure formed by fusion of stamen and pistil), tri-lobed with the apical lobe much larger than the lateral lobes and terminally cleft, with a large, basal callus adnate (fused) to the column.

Fig. 7. Pl 0137, Orchids of Peru. Photo: DSC_4447; Thur-19Jan12.

Fig. 8. Close-in of flower, frontal aspect. Photo: DSC_4408; Tues-29Nov11.

Fig. 9. Zelenkoa onusta (Ldl.) Chase & Williams 2001. Front Cover Photo: DSC_3761; Thur-03Sept10.

Now compare the description of the flower with the Icones illustration (Fig. 7), and close-in figures of the flower (Fig. 8) and part of an inflorescence (Fig. 9).

Column short, swollen apically, without a tabula infrastigmatica (a particular form of enlarged column base with a peculiar structure found in some genera of Oncidinae), with a pair of terminal column wings that partly cover the apex; stigma (female portion) round, anther (male portion) terminal, operculate (with a lid at its tip), incumbent (leaning), one-celled; anther cap hinged; pollinarium with two hard, waxy pollinia, with an obvious, abaxial ventral suture, attached to the middle of the saddle-shaped head of the stipe (supporting stalk) by irregularly shaped viscin (caudicles) (being the sticky substance forming threads uniting pollen grains), viscidium oval in outline (the structure that contains the viscin), the stipe is tubular throughout most of its length but open to the abaxial side terminally.

Capsules and seeds not seen. Seedlings not seen.


Alrich, P. and W. Higgins. 2008. Illustrated Dictionary of Orchid Genera. The Marie Selby Botanical Gardens Sarasota, FL. 482pp.

Baker, M. L, and C. O. Baker. 2006. 2006. Orchid Species Culture. Oncidium/Odontoglossum Alliance. Portland, Oregon: Timber Press. 992pp.

Dodson, C. H. and David E. Bennett, Jr. 1989. Icones Plantarum Tropicarum Series II. Fascicle 2. Orchids of Peru. Part 2. Pl 0137.

_______, and Piedad Marmol de Dodson.1980. Icones Plantarum Tropicarum Series II Fascicle 2. Orchids of Ecuador. plates 101-200.

Little, R. J. and Eugene C. Jones. 1980. A Dictionary of Botany. New York: Van Nostrand Reinhold Company. 400pp.

Jackson, B. D. 1928. A Glossary of Botanic Terms. 4th ed. (reprinted 1953). New York: Hafner Publishing Co. Inc. 481pp.

Pridgeon, A. M., ed. 1997. The Illustrated Encyclopedia of Orchids. Portland Oregon; Timber Press. 304pp.

_______ , P.J. Cribb, M. Chase, F.N. Rasmussen, (eds.) 2009. Genera Orchidacearum. Vol. 5. Orchidoideae Epidendroideae (Part two). Trustees of The Royal Botanic Gardens, Great Britain: Oxford University Press. 585pp.

Schweinfurth, C. 1961. Orchids of Peru. Fieldiana. Vol. 30, no. 4. Chicago Natural History Museum. March 31, 1961. pp. 787-1005.

Williams, N.H., M. Chase, T. Fulcher, and W. Whitten. 2001. Molecular Systematics of the Oncidinae Based on Evidence from Four DNA Sequence Regions: Expanded Circumscriptions of Cyrtochilum, Erycina, Otoglossum, and Trichocentrum and a New Genus (Orchidaceae). Lindleyana 16(2) 113-139.

Zelenko, H. 1997. (M. Chase, ed.) The Pictorial Encyclopedia of Oncidium. New York City: Zai Publications. 164pp.

Copyright © 2012 Wilma J. Ferry