Summary. Karyotypes of the seven Pyrrhocactus species were studied for the first time with Feulgen staining and CMA/DAPI banding. All showed 2n = 22 (x = 11). The karyotypes were symmetrical with 9m + 2sm pairs, excepting P. catamarcensis with 8m + 2sm + 1st pairs. They had a terminal microsatellite on short arms of pair #1. Pyrrhocactus bulbocalyx possessed a second satellited pair (#2) exclusively detected with Feulgen. Increasing asymmetry was associated with a decline in karyotype size. Fluorochrome banding, applied for the first time in Cactaceae, revealed that nucleolar chromosome pair #1 had one CMA + /DAPI -terminal band in all species related to the nucleolar organizing region; additional pericentromeric bands were found. A pattern of homogeneous sized chromosomes with median and submedian centromeres is conserved in the genus. However, karyotypes can be distinguished by a combination of cytogenetic features. Species diversification in Pyrrhocactus has not been associated with large chromosome rearrangements or polyploidy, but with cumulative small and cryptic structural changes.

Opuntia series Armatae is evaluated considering morphological (vegetative, floral, and carpological) and cytogenetical (diploid number, presence of heterochromatin, and physical localization of ribosomal genes) features to shed light on their systematics and evolution. Three complexes (named O. elata, O. megapotamica, and O. monacantha) are proposed to accommodate seven species according to the tepal, fruit, stigma, and seed aril traits. Additional systematic conclusions include the following: (i) O. stenarthra, O. assumptionis, O. cognata, and O. subsphaerocarpa are synonyms; (ii) O. elata is a variable species with two varieties (var. cardiosperma and var. obovata); (iii) O. rioplatense is a synonym of O. elata var. obovata; and (iv) O. megapotamica is a polymorphic species with two varieties (one newly described and a new combination). All species had small similar-sized symmetrical chromosomes and were tetraploid (2n = 44), except for a population of O. arechavaletae and O. monacantha (2n = 22). All showed one or two pairs with CMA+/DAPI− NOR associated bands. The 18–5.8–26S rDNA loci seem to coincide with CMA+/DAPI−/NOR blocks. The number of 5S signals detected was proportional to the ploidy level of the species. A combination of cytogenetic and morphological features helped to differentiate the complexes, species, and varieties of Opuntia ser. Armatae.

Karyotype analyses in members of the four Cactaceae subfamilies were performed. Numbers and karyotype formula obtained were: Pereskioideae = Pereskiaaculeata(2n = 22; 10 m + 1 sm), Maihuenioideae = Maihuenia patagonica (2n = 22, 9 m + 2 sm; 2n = 44, 18 m + 4 sm), Opuntioideae = Cumulopuntia recurvata(2n = 44; 20 m + 2 sm), Cactoideae = Acanthocalycium spiniflorum (2n = 22; 10 m + 1 sm),Echinopsis tubiflora (2n = 22; 10 m + 1 sm), Trichocereus candicans (2n = 22, 22 m). Chromosomes were small, the average chromosome length was 2.3 μm. Diploid species and the tetraploid C. recurvata had one terminal satellite, whereas the remaining tetraploid species showed four satellited chromosomes. Karyotypes were symmetrical. No CMA^–/DAPI⁺ bands were detected, but CMA⁺/DAPI^– bands associated with NOR were always found. Pericentromeric heterochromatin was found in C. recurvata, A. spiniflorum, and the tetraploid cytotype of M. patagonica. The locations of the 18S-26S rDNA sites in all species coincided with CMA⁺/DAPI^– bands; the same occurred with the sizes and numbers of signals for each species. This technique was applied for the first time in metaphase chromosomes in cacti. NOR-bearing pair no.1 may be homeologous in all species examined. In Cactaceae, the 18S-26S loci seem to be highly conserved.

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Tephrocactus comprises species mainly endemic to Argentina. Molecular phylogenetic analyses of all proposed species of the genus as well as classical (chromosome number, karyotype) and molecular cytogenetical techniques (DNA content, heterochromatin amount, rDNA genes) were conducted. Sequence data of two plastid DNA markers of Tephrocactus taxa were analyzed. Evolution of character states of cytogenetical and morphological (growth form, presence of leaves, glochids and tepal spiny mucrons, flower color) traits were reconstructed. Species show x = 11 with different ploidy levels (2n = 22, 44, 66, 77, 242, 319), small chromosomes, and symmetrical karyotypes. Tephrocactus was recovered as monophyletic with three main clades including 12 species, using molecular and morphological data. Tephrocactus geometricus, T. halophilus, and T. paediophilus are recognized as distinct species. Banding patterns showed CMA + /DAPI − constitutive heterochromatin associated with nuclear organized regions. Heterochromatin amount ranged from 2.99% to 6.50%. The 18S-5.8S-26S ribosomal DNA (rDNA) sites coincided with the CMA + /DAPI − signals. The 5S sites varied with ploidy levels of the taxa. DNA content (2C = 1.99-24.50 pg) had a significant and positive correlation with ploidy level and the number of rDNA genes. The ancestor is reconstructed to have been a dwarf shrub with strong articulation, glochids, and deciduous leaves, white, pink or pearly tepals without spiny mucrons, 2n = 22, low DNA content, and one pair of each rDNA gene followed by three polyploidization events. Tephrocactus diversification has been associated with polyploidy and few cumulative small cryptic chromosomal changes.

Germination characteristics are important for understanding how species cope with environmental variation. The aims of this work were to analyze the effect of different temperatures (25 and 32 °C), water potentials (0, −0.2, −0.4, and −0.6 MPa), and light conditions (light vs. darkness) on the germination of five populations of the cactus Gymnocalycium monvillei (Lem.) Britton & Rose along its entire altitudinal distribution. The experiments to assess the effects of temperature, water potential, and light conditions were performed in germination chambers, and total germination (%) and mean germination time (T50) were recorded. Germination decreased in provenances from higher to lower altitudes, and the effect was very pronounced at temperatures of 32 °C. For all of the altitudinal provenances, germination decreased with lower water potential, with this effect being more pronounced at 32 °C. On the other hand, provenances at lower altitudes were less affected by lower water potentials than higher provenances. Provenances at all altitudes showed very low germination under dark conditions. T50 did not vary among altitudinal provenances at a temperature of 25 °C, but at 32 °C germination was slower at intermediate altitudes. Our results show that germination characteristics differ considerably among altitudinal provenances and seem to be important in determining the capacity of the species to inhabit such a broad gradient.

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