BRASSIA ALLIANCE

INTRODUCTION

Within the Oncidiinae tribe of orchids are the two closely allied genera of Ada and Brassia. The genus Brassia in particular includes a number of plants which produce spectacular 'spider' like flowers, and which are comparatively easy to grow. Most species produce flowers which give off a pervading pleasant fragrance, especially during warm daylight hours, which is an added attraction. For many years they have not been especially popular plants, but are now being recognised for their true worth. Some hybridisation within the genus has taken place in comparatively recent years, with also some intergeneric breeding completed, in some cases producing most interesting results.

As will be discussed later, the genus Brassia contains plants which fall into two main groupings, one of which shows many characteristics which distinguish plants of the genus Ada; therefore this review from available literature will cover both these genera.


Brassia longissima

The genus Brassia was founded by the English botanist Robert Brown in 1813. It was named in honour of William Brass, a botanical artist and collector for Kew Gardens in the early decades of the nineteenth century. It is ironical that as Brass collected mainly in South Africa, he was never in fact involved in the Central and South American genus that bears his name. The first descriptions were on the basis of the species B. maculata, which had been imported from Jamaica in the early part of the century (1806), and which was the first species to be cultivated in Europe. Since the founding of the genus, some 74 species have at some stage been described as Brassias. The majority of these have now, however, been reduced by synonyms in recent taxonomic studies, with only 2 to 3 dozen valid species remaining.

In 1863 Reichenbach f. transferred all the Brassias then known into the genus Oncidium. Lindley in 1853, confirmed that the distinction between the genera Brassia and Oncidium was slim. Brassias are distinguished by their very short earless column, and a lip which is not lobed, bearing a callus of two parallel ridges, combined with elongated lateral sepals. Because of their readily distinguished flowers, most botanists have continued to maintain the Brassias as a separate genus, to save endless confusion with labels which would arise if amalgamation was confirmed, and partly because there appears to be a distinction readily apparent to most growers.

Two major groupings of somewhat similar species of Brassias can be identified, and in 1853 Lindley sectioned the genus into the Eubrassia ('true brassia'), similar to B. maculata, and the Glumacea, similar to the species B. glumacea. The sections are distinct, the most obvious distinguishing characteristic being the large papery floral bracts of the Glumacea, which sheath the pedicel completely as compared with the small basally clasping bracts of the Eubrassia. The Eubrassia have prominent pseudo-
bulbs with 2 to 3 basal bracts, which never sheath the mature pseudobulbs. The Glumacea produce, on well grown specimens, 2 to 3 inflorescences per growth; the Eubrassia only 1, or rarely 2.

The natural habitats also appear to confirm the establishment of the two subgenera. The Eubrassia extended at one time from Florida throughout central America to northern America, principally in lowland fairly dry tropical areas, although one species, B. verrucosa, is frequently encountered in high elevation cloud forests. The Glumacea species are generally only localised in these higher elevation cloud forests.


In reviewing this genus, botanists found that the features which serve to distinguish Eubrassias from the Glumacea are similar to the characteristics of the genus Ada. While this affinity is recognised, the genus Ada has not generally been amalgamated with the Brassia glumacea species, although Williams, in 1972, did take this step.


The genus Ada was founded in 1854 for the single Andean species A. aurantica. There seems to be little affinity between the Glumacea and Ada based on external flower form. However, on opening up Ada auranticia, a flower is discovered con- forming in many ways to the Glumacea, except in its colour.

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 Site established 9th May 1998
Oncidium series first uploaded 20 October 1999