Roberto Kiesling,Instituto Argentino de las Zonas Áridas; Laura Las Peñas, Universidad Nacional de Córdoba (Argentina) & Luis Oakley, Universidad Nacional de Rosario (Argentina).
The BCSS Research Committee has given us a grant to be used for field trips and laboratory expenses, to study the overlooked genus Tunilla.
The genus Tunilla, published by Hunt and Illiff (Cact. Syst. Init. 9: 10. 2000), has received little attention and there is no single work to help recognize the different taxa apart from a tentative key by Illiff in Hunt & Taylor, Studies on Opuntioideae: 164. 2002). D. Hunt stated in his Bulletin (Cact. Syst. Init. 35: 30. 2016): “… James Iliff and I named the genus, and we boldly made new combinations for a dozen of the relevant taxa, but I’m obliged to admit it is taxonomically one of the most poorly understood, if not the most poorly understood, in the entire family.” That is absolutely true: both amateurs and professional botanists neglect it, even more so than other Opuntioids.
The genus is mainly Bolivian and Argentinian, with some species near the Peruvian border with Bolivia and the extreme North of Chile. In Argentina it has a relatively narrow E-W extension (100-200 km). However, it extends for around 1200 km in latitude, along the Andes and other more or less parallel lower mountains, from the Bolivian border to South Mendoza. It has also been mentioned further South in Neuquén province.
We have long kept in cultivation some 20 samples with registered field localities, and recently some 25 more have been incorporated, thanks to permits to collect in three NW Argentinian provinces. Provisional field observations indicate there are basically two main species groups: the ones with spherical, ovoid to cylindrical segments, and the ones with more or less flat segments, each having a characteristic branching pattern. Each group apparently has several species.
We aim to study the genus both using classical taxonomy methods based on morphology plus the unavoidable nomenclatural matters (Kiesling and Oakley) and using chromosomes and a molecular study (Las Peñas). The intention is to prepare a taxonomic treatment, with a complete description of the taxa we recognize, the correct name of each species or subspecies, synonyms, field observations, a key for the taxa, locality, habitat, and environmental field conditions.
The trips will be made in the flowering and fruiting seasons: between late November and mid- to late February (spring and summer at the South hemisphere). Also, samples in cultivation wil be used to show us how plants from different areas develop in a uniform environment.
As these plants often reproduce by detached segments, due to the typically fragile joints between segments, and animal damage, many populations are clonal. In such circumstances, a single clone occupying a wide area can be interpreted as a species, while two clones of one species can be taken as two different species. The laboratory analysis should help in the interpretation of such cases. To mention one example: around Mendoza (near where one of us lives) there are many colonies of Tunilla corrugata with small very spiny spherical segments, and less frequently, there are colonies with bigger, less spiny flat segments. The flower color – as observed so far – is consistently deep red in the first case, but variable in the second. Comparison of chromosomes and DNA sequences of both can indicate how closely they are related.
Although this study is limited to Argentina, we assume the delimitation of species can be also used for Bolivian species, or help to recognize others if they exist. The finding of consistent characters is possibly the most important point, as in all botanical taxonomy.
A, B: Tunilla corrugata near Mendoza city, with nearly spherical segments and dense, relatively short spines, as well consistently deep red flowers.
C, D: Close to T. corrugata there are other colonies with flat segments and flowers of variable color, from orange to yellow.
E: Plants from Catamarca with small disk-shaped segments and short spines agree well with the original description of Opuntia microdisca (now Tunilla microdisca) from this province.
F: Tunilla cf. albisaetacens had been found in the Jujuy Puna, with the typical red fruits of the genus, used to give color to food, drinks and clothes.
G,H: Tunilla cf. erectoclada lives in the same area as T. albisaetacens, but is more abundant. Its segments resemble those of T. soehrensii, but are elongated and form a chain, while those of T. soehrensii form lateral branches and are not elongated. Are they different clones of the same species?
I: Tunilla sp. at Tucumán, Los Cardones. It resemblesT. corrugata, which is known from Mendoza to La Rioja.