A wild orchid

The orchid Pleione humilis was very common in and around the upper reaches of the Neora Valley national park. All along the eastern Himalayas at altitudes between about 2 and 3 Kms above sea level, it is in flower in late winter and early spring. I’ve been to the right height also in Sikkim, Bhutan, and Assam, which are all parts of the normal range of this orchid, but missed the flowering because I usually go later in spring. The orchid grows on wood or moss, and likes to spend about a quarter of the day in sunlight, so the drooping white flowers are easily visible along roads. Each flower grows out of a different bulb, and each bulb has only a single leaf.

I’d noticed earlier that orchid fanciers are like orchard managers. Interested in tiny differences between varieties, and paying great attention to their differentiation. The greatest achievement that enthusiasts can think of is to have a variety named after them. This exasperates botanists, which is very evident when you read a paper from 1971 in the Kew Bulletin called The Cytology and Taxonomy of the Genus Pleione. Hunt and Vosa, the authors, write “About forty specific epithets have been published in the genus Pleione and considerable confusion exists among the names given to plants in cultivation. Understandable and acceptable differences of taxonomic opinion were confounded with outright mis-identification.” You don’t get more sarcastic in a scholarly publication! They conclude that there is no evidence for more than nine species in the genus Pleione.

Following the thread on cytology, I looked at a very interesting observation in a thirty years-old paper. There seem to be two different growth “habits” among Pleione species. Some are epiphytic, meaning they grow on trees or moss. The Pleione humilis in the featured photo is one of these. The others, which I haven’t seen, are terrestrial, meaning they grow on the ground. The habit depends on the shape of the chromosomes. Paired chromosomes are linked by a structure called a centromere. When this is at the middle of a pair, they are called metacentric chromosomes. Human chromosomes are metacentric, as a result of which the chromosome appears to be in the shape of an X when you see it in a microscope. When the centromere is at the end of a pair, then their visual appearance in a microscope is like an I. These are called telocentric chromosomes, and are rather uncommon in plants. The paper found that epiphytic Pleione have metacentric chromosomes, whereas the chromosomes of the terrestrial species in the genus are telocentric. I haven’t found papers which followed this up in the modern age of genomic analysis. Perhaps there are new taxa hiding in this genus.

By I. J. Khanewala

I travel on work. When that gets too tiring then I relax by travelling for holidays. The holidays are pretty hectic, so I need to unwind by getting back home. But that means work.

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