Molecular sequence data from the 18S‐26S rDNA internal transcribed spacer (ITS) region support the monophyly of Fouquieria sensu lato (Fouquieriaceae) and the three subgenera (subg. Fouquieria, subg. Bronnia, subg. Idria) previously recognized within it. Resolution within subg. Fouquieria differs somewhat between parsimony and maximum likelihood (ML) trees. Section Fouquieria and sect. Ocotilla within subg. Fouquieria are not well supported as monophyletic groups. Uncertainty regarding placement of the root within Fouquieriaceae makes discussion of character evolution within the family difficult. Three root positions are consistent with rate-constant evolution of ITS sequences: (1) along the branch to subg. Idria, (2) along the branch to subg. Bronnia, and (3) along the branch to subg. Fouquieria. The first root position listed is equivalent to an outgroup rooting. The third root position listed is equivalent to a midpoint rooting. Of the three root positions above, only the third is along a branch that may be sufficiently long to act as a long-branch attractor. The first two root positions would result in character reconstruction suggesting that succulent growth forms and white floral pigmentation are ancestral within the family, with shifts to woody growth forms and to red floral pigmentation. The third root position results in equivocal reconstruction of the ancestral growth form, equivocal reconstruction of ancestral floral pigmentation in parsimony trees, and a suggestion of white floral pigmentation as ancestral in ML trees. Two previous hypotheses of polyploid origins are compatible with the molecular data presented here: (1) origin of the tetraploid F. diguetii from F. macdougalii, and (2) allopolyploid origin of the hexaploid F. burragei from the tetraploid F. diguetii and a diploid species similar to F. splendens. Direct descent of the hexaploid F. columnaris from the subg. Bronnia lineage is not supported by our data. An amphiploid origin of F. columnaris involving a member of the subg. Bronnia lineage and an extinct taxon outside subg. Bronnia, however, cannot be ruled out.

https://bsapubs.onlinelibrary.wiley.com/doi/pdf/10.2307/2656819

Molecular phylogenetics of Fouquieriaceae: evidence from nuclear rDNA ITS studies.

Crassulacean acid metabolism (CAM) is a photosynthetic adaptation to water and/or CO2 limited environments that has evolved in 400 genera from 36 families of higher plants. Despite the taxonomic and ecological diversity of CAM, plants with this photosynthetic specialization share a number of common anatomical traits that impinge on the physiological processes underpinning photosynthetic CO2 assimilation and water use. Thick, succulent leaves and/or stems are typical for terrestrial CAM plants. The large cells within these succulent tissues serve to accommodate the overnight vacuolar accumulation of malic acid that defines CAM and also increase water storage capacity. Significant morphological and anatomical diversity exists among leaf and stem succulents that impact on water-use strategies and thus the predisposition towards CAM. We provide an overview of CAM diversity in terms of leaf and stem anatomy, leaf venation and stomatal patterning. We consider the physiological implications of these anatomical traits in terms of water use and leaf hydraulic properties as well as the impacts on CO2 uptake and carbon gain. We also discuss which anatomical traits are likely to be important determinants for the mode and level of CAM that might be engineered into non-CAM species as a means of improving plant water use efficiency.

Functional Anatomical Traits of the Photosynthetic Organs of Plants with Crassulacean Acid Metabolism

https://sdnhm.org/oceanoasis/brcc/reprints/67.pdf

Functional morphology and evolution of stem succulence in cacti

Cephalocereus columna-trajani is a giant columnar cactus endemic of the Tehuacan-Cuicatlan Valley in Central Mexico. Stem tilting and northward pseudocephalium azimuth in C.␣columna-trajani have functional advantages in terms of interception of direct solar radiation at the northernmost portions of its range. Since the success of both characters strongly depends on the apparent position of the sun during the growing season, in this paper we test the hypothesis that the occurrence of such columnar morphology is restricted geographically and imposes mechanical restrictions that limit column height. Following a latitudinal gradient along the Tehuacan-Cuicatlan Valley, we selected five populations, recorded tilting angle and pseudocephalium azimuth, and carried out allometric and biomechanical analyses of height–diameter relationships. Northern populations showed higher tilting angles. Pseudocephalium azimuth significantly differed among populations, and pseudocephalium orientation was consistently North-Northwestern. Stem allometry showed that the stems of the southern populations increased in height at a far greater rate with respect to diameter than the northern populations. The southernmost population showed the lowest safety factor. These results support the hypothesis that stem tilting in C.␣columna-trajani is functionally advantageous in a restricted geographical range, and imposes mechanical restrictions to column height.

Stem tilting, pseudocephalium orientation, and stem allometry in Cephalocereus columna-trajani along a short latitudinal gradient

Wood lignin composition strongly depends on anatomical features and it has been used as a marker for characterizing major plant groups. Wood heterogeneity in Cactaceae is involved in evolutionary and adaptive processes within this group; moreover, it is highly correlated to the species growth form. Here we studied the lignin structure from different types of woods in four Cactaceae species with different stem morphologies (Pereskia lychnidiflora, tree/fibrous wood; Opuntia streptacantha and Pilosocereus chrysacanthus, tree/succulent fibrous wood; Ferocactus hamatacanthus, cylindrical stem/dimorphic wood) in order to determine their relationship with the wood anatomy in an evolutionary-adaptive context. Dioxane lignin was isolated and analyzed by pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS), two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The main linkages are the β–O–4′ ether (67-85%), the β–β' resinol (10-26%) and the β–5′ and α–O–4′ linkages of the phenylcoumaran structures (≤ 7%). Spirodienone structures have a considerable abundance (5%) in the dimorphic wood of F. hamatacanthus. In addition, low contents (≤ 3%) of α,β-diaryl ether, α-oxidized β–O–4′ ether and dibenzodioxocin structures were found. The sinapyl- and coniferyl acetates are not part of the wood lignin in any of the studied species. The low (≤ 5%) γ-acetylation in the F. hamatacanthus and P. chrysacanthus wood lignin is here interpreted as an evidence of a high specialization of the wood elements in the conduction/storage of water. The lignin of the studied Cactaceae is composed predominantly of guaiacyl and syringyl units (S/G: 0.9-16.4). High abundance of syringyl units (62-94%) in three of the four species is considered as a defense mechanism against oxidative agents, it is a very conspicuous trait in the most succulent species with dimorphic wood. Furthermore, it is also associated with ferulates and the herein called γ-acetylated guaiacyl-syringaresinol complexes acting as nucleation sites for lignification and as cross-links between lignin and carbohydrates at the wide-band tracheid-fiber junctions.

/pdf/structural-characterization-of-lignin-in-four-cacti-wood-47t7r5glvz.pdf

A. Altesor

Papers

Allometric neoteny and the evolution of succulence in cacti