Boletín de la Sociedad Argentina de Botánica Volumen XV, N° 1 (Enero 1973), págs. 72-76) INTERSPECIFIC HYBRIDIZATION IN FEEGIAN CALTIIA L. D. M. MOORE 1 AND R. N. P. GOODALL 2 SUMARIO Se describe un híbrido natural entre Caltha appendiculata Pers. y C. dioneifolia Hook. f. Este híbrido es muy raro, parece estéril y tiene caracteres intermedios entre las dos especies. Es el primer híbrido interespecífico citado para el género. INTRODUCTION The temperate genus Caltha has a circumboreal distribution in the Northern Hemisphere, where up to some 12 species have- been recognized in Eurasia and North America, depending upon the degree of splitting of the C. palustris complex. The Southern Hemisphere species all belong to section Psychrophila DC. (Hill, 1918), characterized by the distinctive leaf-appendages, 4 species occurring in the Australian-Neozeelandic region (Hill, 1918) and 3 in temperate South America (Lourteig, 1952). So far as we are aware no case of natural interspecific hybridization has been reported within the genus, and certainly not between any species of sec¬ tion Psychrophila. Three species are present in Tierra del Fuego: Caltha sagittata Cav., C. appendiculata Pers. and C. dioneifolia Hook. f. All occur in moist habitats, C. sagittata usually preferring wetter seepage areas with mineral soils, while the other two species normally grow in hummock-bog areas, frequently in association with Astelia or Sphagnum. Because of the dif¬ ferent ecological preferences, C. sagittata rarely grows together with other species of the genus, although sometimes it is mixed with C. appendicu¬ lata. On the other hand in the southern part of the Isla Grande of Tierra del Fuego and some other islands C. appendiculata and C. dioneifolia very commonly occur intermingled in the widespread bog communities which replace the Nothofagus forest on the middle and lower slopes of 1 Department of Botany, University of Reading, England. 2 Estancia Harberton, Ushuaia, Tierra del Fuego, Argentina. D. M. MOORE AND R. N. P. GOODALL, Interspecific hybridization in Fuegian Caltha 73 ( I \ \ 6> \ \ & / / b \ V / II /, V ,1 fÚ a p li c J_ Fis- !• Leaves of (a) Caltha appendicnlata, (b) C. dioveifolia and— (c) their interspecific hybrid. Scale = 1 mm 74 BOLETíN DE LA SOCIEDAD ARGENTINA DE BOTáNICA, XV (1), 1973 the mountains, as they do in the magellanic moorland (Godley, 1960) which occurs widely in the western Fuegian archipelago, Isla de los Es¬ tados and the eastern tip of Isla Grande. The purpose of this paper is to report the discovery of a natural hybrid between the latter two species, believed to be the first such recorded for the genus. OCCURRENCE AND DESCRIPTION OF THE HYBRID During February 1971 the junior author discovered a patch of Caltha which appeared unusual and was suspected to be of hybrid origin (Goodall 3367 - BAB, LTR, NA). It was found on a steep west-facing slope of Monte Spion Kcp in the Sierra Lucas Bridges (lat. 54° 45' S, long. 67° 13' W) in the southern part of Isla Grande. The presumed hybrid, covering an area of about a square meter, occurred at treeline where the ‘"krumholz” forms of Nolhofagus antárctica give way to a narrow Bolax- Empetrum hummock community which grades into the steep rock screes of the upper slopes. Here locally moist conditions permit the gtowth of an open community containing Senecio acanthifolius, Ourisia fuegiana, Tetracbondra patagónica ssp. fuegiana, Epilobium curminghamii, Caltha appendiculata and C. dioneifolia. Caltha appendiculata and C. dioneifolia can be readily distinguished in a number of characters (Table 1) and further examination of the presu- TABLE 1 Principal character differentiating «Caltha appendiculata » and « C. dioneifolia» and their expression in the presumed hybrid dioneifolia hybrid appendiculata Leaf-lamina Length (mm), 2-4 7-9.5 6-17 Width (mm). 2-4 5.4-8 2-11 Texture Coriaceous ± Coriaceous Herbaceous Margin Involute, ± Involute, Flat, glabrous ciliate ciliate Petiolar sheath Total length (mm) 5-9 7-16 (12-) 15-26 Length aduate to petiole (mm) 1.5-4 4-9 (6-)'8-20 Proportion of petiole expanded into sheath 0.33-0.53 0.44-0.66 (0.4) 0.69-0.85 Perianth segments, length (mm) 3.5-6 5-10 ' Number of stamens . 6-9 '8-10 (-12) D. M. MOORE AND R. N. P. GOODALL, Interspecific hybridization in Fuegian Caltha 75 med hybrid showed it to be intermediate between the two species. In the absence of flowers on the hybrid only vegetative features, particularly those of the leaf-lamina (Fig. 1), could be used but from detailed inves¬ tigation of such characters in it and populations of the two parents from the same region (eg. Fig. 2) it may be presumed to be an FI hybrid. The tendency for the number of leaf-appendages to be greater in the hybrid (2-3(-4)) than in either C. appendiculata ( (0-)2(-4) ) or C. dioneifolia (2) may result from the fact that they arise closer to the base in the latter than the former species and are to some extent being expressed simultaneously in the hybrid. o 10- o o o o o 8 4 4 o o o Lamina :Ao o o width 6 4 4 <9 o (mm.) ®44 4 o o 4 O 2 o 2 4 6 8 10 12 14 16 18. Lamina length (mm.) Fig. 2. Scatter diagram showing the frequency of marginal cilia, and the dimensions of the— lamina in the interspecific hybrid (/\) and two neighbouring populations each of Caltha appendiculata (0) and C. dioneifolia (ÿ). The density of ciliation on the margins of lamina and appendages is indicated as follws white-cilia absent ; black/ white -1-3 cilia/mm ; black -4-8 cilia/mm. Unfortunately it has not been possible to maintain the plant in culti¬ vation so that we have no cnrect information on its reproductive capacity and related factors. However, it may be significant that nQt a single flower at any stage of development could be discovered on the plant, while both the presumed parent species in the immediate vicinity bore flowers and fruits. This suggests that the hybrid is sterile, although able to produce the characteristic extensive"cushion (hummock) by vegetative growth, the uniformity of the hybrid population (Fig. 2) suggesting that it has pro¬ pagated vegetatively following germination of a single hybrid fruit. In one of the two populations of C. appendiculata examined intensively (Fig. 2) an occasional leaf was found to have a few marginal cilia. Whe- 76 BOLETíN DE LA SOCIEDAD ARGENTINA DE BOTáNICA, XV (1), 1973 ther this results from the rare occurrence of the character in this species or indicates that some backcrossing may have taken place requires much fuller study. DISCUSSION A noted earlier, these two Caltha species occur sympatrically over ex¬ tensive areas of cushion bog in the mountains of southern Tierra del Fuego and elsewhere. However, despite repeated observations this, is the only time we have encountered this hybrid. In view of the frequent sympatry of the parents, the hybrid’s undoubted rarity may be due to its inability to compete in the rather closed bog communities, to the infrequency with which the interspecific crossing takes place or to the inviability of the hybrid. It may be significant that the hybrid was found near the upper limit of the bog vegetation, where it is much open than elsewhere, sugges¬ ting that competition is an important factor in its survival, but there is unfortunately little pertinent information on the other possible factors. Both species have the same chromosome number (2 n — 48) and are known to be self-compatible (Moore, 1968 and unpub.). They obtaip a generally high level of fruit set, but there is as yet no indication as to what pollinators are involved or whether a high degree of autogamy might be preventing crossing. Here, then, we Have a rare hybrid, intermediate between the parent species, and apparently an FI generation. It is morphologically clearly recognizable, apparently sterile, but able to propagate vegetatively and to persist in conditions of lowered competition. Because of its rarity there seems no case as yet for assigning a binomial to this distinctive hybrid but it should be sought for in other areas where the two parent species are sympatric. ACKNOWLEDGEMENTS We are grateful to the National Environment Research Council ( D.M.M. ) and the National Geographic Society (R.N.P.G.) for the award of grants during the tenure of which this study was carried out. BIBLIOGRAPHY GODLEY, E. J., 1960. The botany of Southern Chile in relation to New Zealand and the Subantarctic. Proc. Roy. 'Soc. London Ser. B. 152: 457-475. HILL, A. W., 1918. The genus Caltha in the Southern Hemisphere. Ann. Bot. 32: 421-435. LOURTEIG, A., 1952. Ranunculáceas de Sud América templada. Darwiniana 9: 397- 608. MOORE, D. M., 1968. The Vascular Flora of the Falkland Islands. Br. Antarct. Surv. Sc. Rep. N? 60: 202 pp..