Molecular cytogenetic insights into the evolution of the epiphytic genus Lepismium (Cactaceae) and related genera

Changes in chromosome structure and number play an important role in plant evolution. This was investigated in the Neotropical epiphytic cacti: all Lepismium spp. and some related Rhipsalis spp. Both genera have species with disjunct distributions between the paranas of south‐eastern Brazil and north‐eastern Argentina and the yungas forests of the eastern Andes. Karyotypes, fluorescent banding and fluorescence in situ hybridization (FISH) studies using rDNA probes were performed. A time‐calibrated phylogenetic tree was generated to place the karyological information and biogeographical history in an explicit evolutionary context. All species were 2n = 22 and showed symmetrical karyotypes comprising only metacentric chromosomes of similar sizes. The heterochromatin bands were always associated with chromosome satellites coinciding with the location and number of the 18S–5.8S–26S rDNA loci. The 5S rDNA loci had more heterogeneous profiles with one or two loci per haploid genome. Phylogenetic analysis suggested an ancient duplication event of the 5S rDNA loci and more recent post‐speciation translocation and deletion events. These genome restructurings are estimated to have occurred approximately 13.98 Mya in the middle Miocene, after Lepismium and Rhipsalis diverged. The ancestor of Lepismium may have had a similar karyotype to L. lumbricoides and the Rhipsalis spp. (i.e. one 5S locus on chromosome 2). Both genera hypothetically originated in the yungas (north‐eastern Argentina and southern Bolivia), but diversification of the Lepismium crown group probably originated from populations with duplicated 5S loci in the parana forests of south‐eastern Brazil (8.70 Mya in the late Miocene). Two migration events between the yungas and parana forests were suggested to explain the extant distribution of Lepismium spp. These results make Lepismium a model system for the study of the complex chromosomal evolution in plants. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 263–277.     

A macro- and micromorphological survey of floral and extrafloral nectaries in the epiphytic cactus Rhipsalis teres (Cactoideae: Rhipsalideae)

Floral and extrafloral nectaries in plants favor pollination and defense against herbivory. Despite their wide distribution in plants and differences in position, structure, and topography, their biological and systematic significance has been underutilized. This study investigated the macro- and micromorphology of floral and extrafloral nectaries in the epiphytic cactus Rhipsalis teres and reports unusual bristle-like structures (bracteoles) functioning as extrafloral nectaries in the cactus family. The floral nectary is disc-shaped embedded in the hypanthial floral cup with anomocytic stomata as secreting structures present on the epidermal nectarial tissue. Small multicellular bristle-like extrafloral nectar-secreting structures, homologues to bracts, were observed on the plants’ stems and function as bracteolar nectaries having a relatively long and continuous secretory activity throughout several stages of the reproductive structures. Both the floral and bracteolar nectaries are functional. It is possible that in the latter nectar discharge occurs though epidermal cells, which build up pressure inside as nectar accumulates, thereby ending with rupture of the cuticle to release the liquid. The nectar in both secreting structures is scentless and colorless, and the concentration from floral nectaries is slightly lower than that of the bracteolar nectaries, 70.6% and 76.4%, respectively. The relatively higher concentration in the latter might be correlated with exposure, relative humidity and water evaporation, leading to crystallization of sugars on the stem surface in a short period of time.     

Diel patterns of CO2 exchange for epiphytic cacti differing in succulence

Net CO: uptake over 24-h periods was examined for 6 species of epiphytic cacti. which as a group number about 120 species that vary considerably in stem succulence. Nocturnal CO, uptake as a percentage of the total daily CO, uptake increased from 0% for Rhipsalis houlletiana to 14% for Epipliyl/urn pittieri to 21% for E. oxypetnluin to 51% for R. rhornbea to 87% for Schlumbergera truncata to 98% for Cryplocercus anthonyamis. For R. houlletiana and S. truncata, maximum net CO, uptake occurred at a photosynthetically active radiation of only 200 μmol m⁻² s⁻¹, as is typical for shade plants. Short-term drought of R. rhombea caused a shift favoring nocturnal CO, uptake. For the 6 species examined, increased reliance on nocturnal CO, uptake characteristic of Crassulacean acid metabolism (CAM) was closely correlated with increases in stem thickness, fresh weight per unit area, water mass per unit area, and to a somewhat lesser extent with another measure of succulence, water mass per unit mass of chlorophyll.     

Spider communities in two plant architectures of epiphytic cacti in the Brazilian Atlantic forest

The vegetative architecture of the Cactaceae provides sites used by spiders as hideout, foraging, mating and oviposition. We found more web weavers in plants with cylindrical cladodia and more hunters in plants with flat cladodia. Between February 2014 and January 2015 1551 spiders distributed in 20 families were collected: one of these families, Palpimanidae, had only juvenile individuals collected; of the other 19 families, 80 species/morphospecies were identified. This work aims to contribute to the knowledge of biodiversity in the canopy of the Atlantic Forest, especially the relationship between cacti and spiders.     

A unique cactus with scented and possibly bat-dispersed fruits: Rhipsalis juengeri

Rhipsalis juengeri was described in 1995 as an unusual representative of epiphytic cacti, forming more than 3 m long curtains, hanging from the canopy of the Atlantic Rainforest in eastern Brazil. At the apex of thin, pendant shoots, green-brownish berries are formed. We report here as a novelty for the Cactaceae that these berries are strongly scented, and present an odour analysis along with an olfactoric survey of fruits of about 50 species and varieties of the cactus tribe Rhipsalideae. The volatile blend of berries of R. juengeri is dominated by ketones, some of which are responsible for the characteristic blackcurrant-like scent, as is shown by GC-olfactometry. The odour and inconspicuous colour stand out among fruits of other epiphytic cacti that are thought to be consumed by birds. Fruit characters of R. juengeri and the flagellicarpic presentation indicate adaptation to chiropterochory.