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Anderson et al. unpubl.), morphological features that have linked them with similar species from Mexico (Whalen 1984). More recent work has indicated a geographically * Corresponding author: phone (Fax) ++54

351 4331056;

e-mail: [email protected] more logical linkage with African solanums (Bohs et al. unpubl.). This species pair is of interest as well in the context of the origin of the taxa. Both species are found on one of the islands (Gran Ca- naria ? older, and closer to the African source for the species) ? thus they are geographically sym- patric in that context (Bohs et al., unpubl.). The somewhat more abundant species, S. vespertilio, is also found on the younger, and more distant (from Africa), Tenerife. Thus, the species may have had a sympatric origin on Gran Canaria, or S. vespertilio may have been derived from the Af- rican progenitors independently, and/ or later, on Tenerife, and then colonized the nearby Gran Ca- naria. Comparative karyotype studies have proved to be useful in determining systematic and evolu- tionary relationships in some Solanum sections (Bernardello and Anderson 1990;

Ber- nardello et al. 1994;

Acosta et al. 2005). This is in spite of the fact that they are generally com- posed of homomorphic chromosomes of small size, and are mostly diploid (Stebbins 1971;

Mo- scone 1992;

Acosta et al. 2005). In this contribution, a morphometric karyo- type analysis has been performed on these two Solanum subgen. Leptostemonum species with the aim of reporting comparative karyotype data for the first time, as well as the chromosome number of S. lidii (the gametic chromosome number of S. vespertilio has been published by Aldridge and Ortega in 1976). The data are employed to un- derstand patterns of chromosome differentiation and taxonomic relationships. MATERIAL AND METHODS The provenance of the plant material studied is: Solanum lidii: Spain, Canary Islands, Gran Ca- naria, Temisas, Anderson and Santos Guerra 4801, 01/June/2004. S. vespertilio: Spain, Canary Islands, Tenerife, Las Bodegas, Anderson and Santos Guerra 4601, 01/January/2004. Vouchers are deposited in the herbarium of the Instituto Canario de Investigaciones Agrarias (ORT) and the George Safford Torrey Herbarium (CONN). Primary roots obtained by germinating seeds were used to study the somatic chromosomes. Root tips were pretreated with paradichloroben- zene-saturated solution for

2 h at room tempera- ture, and then fixed in 3:1 ethanol:acetic acid mix- ture for a minimum of

12 h. Meristem cells were isolated, macerated, and squashed in a drop of 45% acetic acid after staining with alcoholic hy- drochloric acid carmine (Snow 1963) for two hours at 60°C. Slides were made permanent by re- moving the cover slip by freezing with liquid ni- trogen. Thirty five cells of

20 individuals per spe- cies (i.e., a total of

700 cells) were examined under a Zeiss Axiophot microscope. Ten metaphase plates from

10 individuals of each species were photographed with a Leica DFC300 FX digital camera and the photographs were used to take measurements of the following features for each chromosome pair: s (short arm length), l (long arm length), and c (total chromosome length). The arm ratio (r = l/s) was calculated and utilized to classify the chromosomes as recognized by Le- van et al. (1964) as: m ? metacentric (r = 1.00- 1.69) or sm ? submetacentric (r = 1.70-2.99). Battaglia's (1955) terminology for satellites was used. The satellite lengths were added to the lengths of the corresponding arms. In addition, haploid karyotype length based on the mean chro- mosome lengths for each species, average chro- mosome length, and average arm ratio were calcu- lated. Idiograms were based on the mean values for each species. The chromosomes were ar- ranged, as usual, into groups according to their in- creasing arm ratio, and then according to the de- creasing length within each group. Karyotype asymmetry was estimated using the following pa- rameters: A1 = intrachromosomal asymmetry in- dex, which indicates the length difference among the chromosome arms, and A2 = interchromo- somal asymmetry index, which indicates the size variation among the chromosomes (Romero Zarco 1986). RESULTS AND DISCUSSION The somatic chromosome number 2n =