Le specie nane di Iris in Toscana e il loro problema tassonomico

Riassunto

È stato studiato il problema tassonomico di alcune Iris nane [I. lutescens Lam., I. chamaeiris Bertol., I. italica Parl, e I. olbiensis Hén.) conducendo ricerche bibliografiche, di erbario e osservazioni in campagna e in coltura su esemplari provenienti da tutta la Toscana e coltivati nell'H.B.F. L'analisi dei campioni di erbario ha concordato perfettamente con i dati bibliografici ed ha mostrato l'impossibilità di differenziare le quattro specie, più volte dai diversi autori confuse tra loro. L'esame dei dati morfologici, fatto sullo scapo fiorifero, sulle foglie e sul fiore di diversi esemplari raccolti in varie stazioni, ha mostrato che i caratteri ritenuti nel passato fondamentali per la diversificazione delle quattro specie non sono da prendere in considerazione, in quanto essi non sono significativi e non permettono di distinguere le diverse entità. Ciò viene confermato anche dallo studio morfologico dei granuli pollinici dei diversi esemplari eseguito al S.E.M. Del resto anche l'analisi cariologica condotta precedentemente dagli autori (MAUGINI e BINI MALECI 1974, 1975; BINI MALECI 1976) non era riuscita di aiuto nella separazione delle diverse entità. Gli autori dall'esame di tutti questi dati, ritengono pertanto che tali Iris nane debbano essere riunite in un'unica specie il cui nome per ragioni di priorità deve essere I. lutescens Lam.

Problems concerning the taxonomy of some dwarf Irises, growing in Tuscany are investigated. In the literature are reported four different species of the dwarf Irises we examined: I. lutescens Lam., I. chamaeiris Bertol., I. italica Pari, and I. olbiensis Hén. According to these reports and to the study of the « exsiccata » three main lines seem to have been followed by the Authors: a) recognition of these entities as four or three separate species (19th century Italian Authors generally do not take I. lutescens into account); b) recognition of two species, one of which is divided in two varieties; c) recognition of one single species for the three entities.

From the study of the types of the above-mentioned species or of specimens from their locus classicus it is easy to see how more than one species of this group of Irises came to be described. The Authors who first reported them on the basis of a few samples had noticed seemingly important distinguishing characters. In actual fact in their typical forms I. chamaeiris and I. olbiensis (the former rather small, the latter much more vigorous and taller) are quite different. Not so clear are their borders when specimens of the entity described as I. italica are examined. Indeed at times the specimens show a very close resemblance to the typical aspect of I. olbiensis and at times to that of I. chamaeiris. PARLATORE too, felt uncertain about this and suggested checking to see if there were transition forms between his I. italica and I. olbiensis.

When a high number of Herbarium specimens are examined we notice that these are an uninterupted series showing no significant differences although its extremes appear distinguishable. We are therefore led to conclude that the characters considered valid by some authors for recognition at specific level of the entities we studied (height of plant, size of leaves, presence or absence of a stem leaf, one or two-flowered stem) neither allow their separation as species nor any diversification within the species itself. Therefore on the basis of the exsiccata the entities described in the past as separate species can be referred to one single species.

As to the name itself, Italian Authors of the last century mentioned I. chamaeiris, I. italica and I. olbiensis only and overlooked or misinterpreted the earliest I. lutescens described by LAMARCK. The study of its type, kept in Paris, showed that the three above mentioned species were akin to LAMARCK'S plants. Therefore I. lutescens is the right name for the species concerned.

Our morphological studies carried out in living wild plants and on plants grown at the Florence Botanical Garden for a long time, led to two important conclusions: a) the length of the perianth tube is practically constant in all the specimens investigated and appears to be a valid character to distinguish our dwarf Irises from the other dwarf Irises (I. pumila and I. pseudopumila) which have a much longer perianth tube; b) our research has clearly shown that all the groups of Irises we examined are on almost uninterrupted series, definitely excluding that those characters, which till recently were used to classify these entities, have any significance from a taxonomic point of view.

Our palynological study carried out on some specimens by S.E.M. has shown no significant differences between the entities we examined.

To conclude: also on the basis of the morphological analysis all the Irises we studied can be regarded as a large group which is capable of avoiding natural selection through a lively vegetative propagation. In this group are observed plants that show a differentiated aspect, but he it is however not so different to allow any distinction at taxonomic level.

The literature, the study of exsiccata, the morphological analysis on living plants, the palynological examination (and also the karyological analysis previously carried out (MAUGINI and BINI MALECI 1973, 1974; BINI MALECI 1976) lead to the conclusion that the Irises we studied are one species whose name must be, for priority reasons I. lutescens Lam. as reported also by WEBB and CHATER (in HEWOOD 1978).