VARIATION AND EVOLUTION IN SOUTH AMERICAN CLARKIA D. M. MOORE and HARLAN LEWiS Botany Department, University of Leicester and Botany Department, University of California, Los Angeles Received5.V.65 1.INTRODUCTION THEgenus Clarkia (Onagracee), currently considered to contain 36 species, is restricted to the western parts of North and South America (fig. i). The 35 North American species are distributed from Baja California to British Columbia (300N.to 48° N.), most of them occurring in California. The South American populations, which have a smaller though still considerable latitudinal spread (290 30' S. to 42030'S.), comprise a single variable species, Clarkia tenella (Cay.) H. and M. Lewis (Lewis and Lewis, within which four sub.. species have been recognised (Moore and Lewis, i 965b). Clarkia tenella is tetraploid, having n 34 (Hiorth, 1941; Raven and Lewis, 1959) and 2fl32 (Moore and Lewis, i965b). It is placed in section Godetia, together with seven North American species, and shows its closest affinities with the only tetraploid among these, C. davyi (Jeps.) H. and M. Lewis. A study of artificial hybrids between C. tenella and C. davji, together with pakeo-ecological evidence, led Raven and Lewis (i) to hypothesise that the two species were derived from a common tetraploid ancestor which had traversed the tropics by long-distance dispersal during or since the Late-Tertiary and given rise to the populations now comprising C. tenella. Detailed study of the variation within Clarkia tenella was made possible by a field trip to Chile and Argentina during 1960-61 and by subsequent experimental work at Leicester and Los Angeles. The data thus obtained are given here and are used to examine the inter- relationships of the South American populations and the course of evolution within C. tenella. 2. DISTRIBUTIONAND HABITAT Clarkiatenella occurs mainly on the west side of the Andes (fig. 2), ranging from the region around La Serena, Prov. Coquimbo (29° 30' S.) through central Chile to Prov. Osorno (400 30' S.), with a single disjunct occurrence further south on the island of Chiloe (420 S.). The few stations in Argentina lie between Las Ovejas, Prov. Neuquen (37° S.) and RIo Corcovado, Prov. Chubut (420 30' S.), an area which is climatically comparable to north central Chile because it lies in the rain shadow of the Andes. C2 37 D. M. MOORE AND HARLAN LEWIS Clarkia tenella occurs from sea-level to about 1400 m. and on a variety of substrates, varying from almost pure sand or gravel to shaley Fm. i.—Distributionof the genus Claricia. or even rather clay soils, whose common features seem to be that they are reasonably well-drained and bare or but sparsely vegetated. Characteristically it grows in open maquis or scrubby, scierophyllous, VARIATION AND EVOLUTION IN CLARKIA 39 flTENELLA TENUIFOLIA LA SERENA AMBIGUA ARAU CAN A r 0 0 16 TFI T2.3 I2 TI AR 1.2. Al. A 2 AR3 AR4 Fia. 2.—Distribution of the subspecies of Clarkia tenella in Chile and western Argentina. Populations used in the hybridisation programme are indicated by their crossing code (see table 2):Tssp. tenella, TF ssp. tenufoIia, A ssp. ambigua, AR ssp. araucana. 40 D.M. MOORE AND HARLAN LEWIS savannah-woodland communities in areas having light to moderate winter rainfall (4•2-12•6 cm. per month) and rather dry summers (o-z 8 cm. per month). This type of vegetation is well-developed in the Chilean coast ranges and in the Andean foothills, regions where C. tenella is most frequently encountered. These communities have an open scrub composed of such genera as Acacia, Baccharis, Berberis, Cassia, Litbraea, Peumus and Trevoa, with a ground layer largely comprising spring-flowering herbs, many of them annual, and including several aliens from other warm-temperate regions of the Old and New Worlds. In coastal areas, from Prov. Valparaiso northwards, C. tenella often occurs on stabilised sand dunes. It is frequent in open habitats resulting from man's activities—road verges and ditch margins, sandy washes, road and rail cuttings. This is particularly true towards the south, where the Rio Blo-Blo marks the transition to a higher rainfall area (150-250 cm. per annum) characterised by a much more mesic vegetation type, the Valdivian Forest. For example, two populations (AR 3, AR 4) occurring near the town of La Union, Prov. Valdivia, inhabit open, well-drained habitats on the eroding bluffs flanking the flood plain of the Rio Bueno and its tributary the Rio Liollehue. Here, very many plants have spread to bare soil on the banks of a road-cutting and at the margin of a wheatfield. The habitats favoured by Clarkia tenella closely parallel those of the N. American Clarkias. In general, these are associated with well- drained soils of open sites in the oak woodland-savannah and chaparral communities, less frequently with more xcric coastal and desert margin conditions. The northward expansion of such species as C. amwna, C. purpurea and C. rhomboidea, which extend into the higher rainfall areas of the north-western U.S.A. and southern British Columbia, is due to the utilisation of open, well-drained sites. 3.MORPHOLOGICAL AND CYTOLOGICAL VARIATION () Morphology and breeding system Clar/ciatenella varies conspicuously in characters such as habit, leaf shape, petal shape and colour, pubescence, inflorescence structure, hypanthium length, and in characters associated with its pollinating mechanism. On the basis of field and herbarium studies, and cultiva- tion experiments, four taxonomic entities have been recognised, differing in breeding system and in certain morphological characters. Since they intergrade morphologically to some extent, they are most appropriately described as subspecies (Moore and Lewis, i 965b). The characters of the four subspecies are summarised in table r and their distributions are shown in fig. 2. The most southerly of them, ssp. araucana Moore and Lewis, has large flowers and is completely out- crossing, having the receptive stigma raised well above the anthers. It is of robust, well-branched habit and seems to be almost entirely restricted to open, rather "weedy" habitats. Towards its northern VARIATION AND EVOLUTION IN CLARKIA 41 limit, near Concepción, it grows sympatrically with ssp. ambigua (Phil.) Moore and Lewis, which is very similar, though with somewhat smaller petals and a shorter hypanthium. However, ssp. ambigua is self-pollinating and readily distinguished from ssp. araucana because the mature stigma scarcely projects from the hypanthium and never reaches the level of the anthers. The two subspecies are largely isolated by their different flowering periods when sympatric, since ssp. ambigua blooms in November and early December while ssp. araucana does not flower before the end of December. Subspecies tenujfolia (Cay.) Moore and Lewis, has flowers of comparable size to ssp. ambigua but it occurs much further north, typically in coastal localities. It is TABLEi Principal characters distinguishing the subspecies of Clarkia tenella Subspecies Tenella Tenufolia Ambigua Araucana Petal length (mm.) . 8-15 (g-)13-22(-25) (12-)15-18 18-30 Hypanthium length (mm.) 1-3 2-45(-5) 25-5 6-ta Pollinating mechanism .selfing, antherslargely outerossing,selflng, stigmaoutcrossing, stigma in Contact stigma usually v. short, not much exceeding with stigma slightly exceedingreaching anthersanthers ( mm.<) anthers Flowering period. X-I IX-XII XI-XII (early) XII (late)-II Distribution (fig. 2) . N. central to N. central ChileS. central Chile S. central to S. central Chile (coastal) S. Chile Argentina Chromosome number (n) v' 17 17 16, 17 at least partially outcrossing, with the mature stigma usually held above the level of the dehisced anthers. However, many populations have some plants, which constitute the smaller-flowered facies, in- distinguishable from ssp. tenella. Like it they are autogamous, with the dehiscing anthers in contact with the mature stigma, so that pollination is effected at or shortly after anthesis. The small-flowered ssp. tenella is the commonest and most widespread subspecies in Central Chile and the only one in Argentina. There are constant differences in various characters between many populations of ssp. tenella and plants may be glabrous to pubescent, have oblanceolate and truncate to linear and long-petiolate leaves, blue to purple or even "burgundy" red flowers or an elongate to compact inflorescence rachis. This variation cannot be resolved further at present and the pattern un- doubtedly results from the high degree of autogamy producing a series of slightly different biotypes. 42 D. M. MOORE AND HARLAN LEWIS (ii)Cytology Chromosomenumbers have been determined from material cover- ing virtually the whole range of Clarkia in South America (table 2). TABLE 2 Chromosome numbers in Clarkia tenella. Populations used in experimental programme are indicated by their crossing code. Field collections made by Moore. Vowiliers deposited at Los Angeles and Leicester I Crossing Field code Locality (Chile unless indicated) number up. knella fl 17 Tz Prov. Coquimbo, Frai Jorge 212 Ta Prov. Valparaiso, La Cruz, Fundo Lo Rojas 220 T3 Prov. Valparaiso, La Calera, Cuesta Pucalan 224 1'4 Prov. Valparaiso, Granilos, Cerro de Ia Campana 236 T5 Prov. Valparaiso, Limache, Cerro Cruz 239 Proy. Aconcagua, Cuesta de Chacabuco 242 T6 Pros'. Santiago, Cucsta de Chacabuco 240 T7 Pros'. Santiago, Maipi, Qucbrada de Ia Plata 250 T8 Pros'. Santiago, Maipd, Quebrada de Ia Plata 255 Tg Pros'. Santiago, La Ermita ai8 Txo Pros'. Santiago, Cucsta Lo Prado 209 Prov. O'Higgins, Rio Pangal, Callanas 262 Tii Prov. O'Higgins, Rio Pangal, above Coya 267 Tia Prov. O'Higgins, Rio Pangal, above Coya a68 Argentina, Pros'. Rio Negro, San Carlos de Bariloche up. tenujfolia fl '7 Prov. Valparaiso, Rcñaca 201 TFt Pros'. Valparaiso, Nocornes 232 up. ambigua n =17 Prov. Concepción, between Concepcion and Florida 280 At Prov. Concepción, between Concepción and Florida 406 Prov.