Holttum, R.E. 1966. Flora of Malaya, Volume II, Ferns of Malaya. 2nd edition. Government Printing Office, Singapore, pp. 653.
Professor Holttum spent much of his life devoted to the study of ferns, and judging by the language used in this extract, must have been a delightful person to know. This is from Richard Eric Holttum, 1895 - 1990.
We stated above that plants of the same kind constitute a botanical species, and that species are grouped into genera. Each genus has a name, often of Greek origin, in a latinized form. Thus there is a genus called Microlepia (from two Greek words meaning small scale) because the indusium of the sorus in this genus is like a small scale. There are many species of Microlepia, which is a genus found throughout the tropics. Each species has a name of its own, usually formed by adding an adjective, also in Latin form, to the genus name. There is a species called Microlepia puberula, meaning minutely hairy. There is also another species called Microlepia ridleyi, because it was first found by Mr. Ridley; here the species name is not an adjective, but the personal name Ridley in Latin form and in the genitive case. Names of this kind are called binomials.
Next, we have to answer the question: how can we find out what the name Microlepia ridleyi means, or whether a plant we have found really belongs to that specues? A botanical name is only accepted if it has been pubished in a recognised scientific journal or book, and with it a description, which now has to be written in Latin (as an international language). In the case of Microlepia ridleyi, the name was published in the Philippine Journal of Science in 1916 by Dr. E. B. Copeland, with a Latin description. We therefore turn to Copeland's description to see whether our plant agrees with it. If we are in doubt about this, we have a further source of information. When a species is described, a dried specimen of the plant on which the description was based is preserved, and that specimen is cited by the author of the species. In describing M. ridleyi, Copeland cited specimen no. 14208, collected at Ulu Temango in Perak by Mr. Ridley. This specimen had been sent to Manila from Singapore; at the same time, part of Mr. Ridley's specimen was kept in Singapore, and is preserved in the herbarium of the Botanic Gardens. If we look at the Singapore specimen, we have before us part of the same plant from which Copeland prepared his description, and it will supply us with details not mentioned in the description. It will thus help us greatly in deciding whether or not our specimen is M. ridleyi. This original collection of Ridley's is called the type of the species M. ridleyi, and it is ultimately on the type specimens that the stability of plant names depends. For nobody can describe a species in every detail, and sometimes it is not at all obvious what details may prove to be important in establishing differences between one species and another. It is therefore necessary from time to time to consult type specimens and re-describe them, as our knowledge of allied species increases.
It sometimes happens that the same name is given to different plants by different authors. This may cause confusion, and to help in avoiding such confusion it is usual to write the author's name, in an abbreviated form, after the name of the species, in this case Microlepia ridleyi Copel.
Now let us take a more complicated case. In the year 1784 the Swedish botanist Thunberg described a fern which he called Trichomanes strigosum. At that time ferns were grouped in few genera, and had not been intensively studied. Later study showed that the genus Trichomanes should be restricted to a group of delicate ferns with sori of particular structure, and that Thunberg's species was not one of them. The genus Microlepia was established in 1836 by Presl (a Czech botanist) for the ferns we now know by that name, and Presl recognised Thunberg's species as belonging to this genus. He therefore called it Microlepia strigosa. This is indicated by including Thunberg's name in brackets, thus: Microlepia strigosa (Thb.) Presl. The name Trichomanes strigosum may be called the basinym of the species. A great many ferns have had a history like this one, owing to the changes in the concept of fern genera. Some ferns indeed have had names in many genera, given to them by as many botanists.
The second name in the binomial does not change; it is the particular name of the species and must be given to that species in whatever genus we may think right to place it, except ( and here another complication) if there is already another species of that name in the genus. Thus Copeland wished to transfer the species Alsophila commutata Mett. to the genus Cyathea, but previously someone had given the name Cyathea commutata to a quite different fern. Therefore a new species name had to be made for Alsophila commutata Mett., and Copeland called it Cyathea recommutata. Though the species must thus have a new name, its type specimen does not change.
It has often happened that the same species has been named twice, at different times, by different authors. The rule then is that the oldest species-name must be used, in whatever genus that name was given. Thus in 1768 Burmann gave the name Adiantum denticulatum to a common Malayan fern which we now include in the genus Davallia. In 1801 Swartz redescribed the same fern as Davallia elegans, and it was long so known (it is so called in Beddome's Handbook of Indian ferns); but by the modern rules of nomenclature the correct name is Davallia denticulata, which binomial was first used by Kuhn in 1867. The reason why Beddome still used the name D. elegans after 1867 was that for a long time botanists did not agree as to the rule in such cases; some used the oldest species name in the right genus (i.e. in Davallia) and others used the oldest species-name in whatever genus it was given. This difference has been the cause of many name-changes.
This subject could be pursued further, into many greater complexities; for a discussion of these, the reader should consult the special literature upon them. The modern rules are devised with the object of stabilizing names; and it is to be hoped that we are gradually reaching a state in which changes wil be less frequent.
But even when we have followed the rules strictly, and even when we have consulted descriptions and type-specimens, there may be differences of opinion as to the right name for a particular plant or specimen. This may in some cases due to less acute observation on the part of one disputant; some characters of ferns are very subtle and not easy to appreciate. Or it may be due to the fact that the species is a variable one, or we may not know how much variation may be accounted for by differences of environment, or even the age of the plant itself. Naming a fern is not easy; knowledge and judgement are needed, and may take long to acquire.