Taxonomic and cytogenetic studies in Opuntia ser. Armatae (Cactaceae)

Abstract

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.

Beyond endemism, expanding conservation efforts: a relictual Pleistocene distribution and first report of the prickly pear cactus,Opuntia bonaerensis,in Brazil and Uruguay

“…chromosome counts, phenology, pollinators and floral biology, geographical distribution), 5) the absence of detailed studies regarding morphology across the distribution of species, and 6) the deficiency of phylogenetic data (Majure and Puente 2014). However, various efforts have been recently carried out to increase the knowledge of the group across all the range of distribution yielding valuable information to decisions regarding species delimitation (Powell et al, 2004; Majure et al, 2012a, 2012b, 2017; Font 2014; Realini et al, 2014a, 2014b; Las Peñas et al, 2017; Köhler et al, 2018; Martínez-González et al, 2019; Majure et al, 2020). Here, we highlighted the use of multiple approaches, such as molecular data, morphological characters, herbarium and field studies across geographical distribution as powerful tools to reveal accurate species identification in a problematic group.…”

“…Opuntia bonaerensis is easily recognized by an array of morphological features, such as the bright dark-green spathulate to long-ellipsoid stem segments, the acute flower buds with inner orange tepals and green stigma, and the short to long obconic fruits with the purple-wine inner pericarp tissue (Font 2014; Las Peñas et al, 2017) (Fig. 4), whereas the morphologically similar O. elata has oblong stem segments, creamy-white stigma lobes and pyriform fruits with green inner pericarpel tissue.…”

“…Morphological characters were assessed based on commonly used characters for prickly pears identification (e.g., cladodes morphology, habit and growth form, spine production) (Pinkava, 2003, Majure et al 2017), with a special focus on those reported by Font (2014) for the southern South American species, such as bud flower apices, stigma color, and inner pericarpel tissue color. The criteria for identification of southern South American species of Opuntia followed those proposed by Font (2014) and Las Peñas et al, (2017).…”

“…The taxon has a complicated taxonomic history being circumscribed in various ways in seemingly arbitrary taxonomic treatments (Spegazzini, 1905; Britton and Rose, 1919; Spegazzini, 1925; Leuenberger, 2002), which is not uncommon in the taxonomic history of Opuntia (Hunt, 2002). Just recently, in the taxonomic revision of the Opuntia series Elatae, O. bonaerensis was resurrected as an endemic species of the Argentinian pampean region and delimited using a set of diagnostic morphological characters that have been historically ignored for southern South American species, such as bud flower apices, stigma colors and color of the inner pericarpel tissue (Font 2014; Las Peñas et al, 2017). The species was further included in a preliminary phylogenetic study of the southern South American species of Opuntia , confirming it assignment to this taxonomic series (Realini et al 2014b).…”

Variation in chromosome number and breeding systems: implications for diversification in Pachycereus pringlei (Cactaceae)

“…In plants, metacentric chromosomes are fairly common, e.g., Araceae (Turco et al 2014), Arecaceae (Oliveira et al 2016) and Asparagaceae (Chen et al 2017), and originate by the fusion of two telocentric chromosomes with relatively little effect in gene sequence (Stebbins 1971). In the Cactaceae, symmetric karyotypes are also ordinary, e.g., Echinocereus (Cota and Wallace 1995), Nyctocereus (A. Berger, 1905) Britton & Rose, 1909 (Palomino et al 1988), Setiechinopsis Backeberg, 1950 (Las Peñas et al 2011), Opuntia Ser. Armata (Las Peñas et al 2017), and other species exhibiting low degree of variability in karyotype morphology. Hence, the morphological homogeneity of chromosomes in P. pringlei is not surprising.…”