Epidermal micromorphology in D ioon : did volcanism constrain D ioon evolution? (original) (raw)
Related papers
Flora, 2018
Anatomical descriptions can be effective for solving systematic issues, but these studies are relatively scarce for cycads. Therefore, we present here a leaflet and cuticle anatomical study on the genus Dioon, to provide a set of epidermal traits that clarify species delimitation and relationships between species and their habitats. We used standard micro-technique for leaflet sectioning, and cuticular peel preparation for light microscopy. Also, we used the chromium trioxide method for scanning electron microscope observations on cuticles. Measurements were taken on 10 randomly chosen replicates of each cell or tissue type, for each of the leaflets sampled per taxon. Micromorphological variation among species was calculated for each trait. Finally, we reconstructed the ancestral states of the observed epidermal fibre-like cell and pore shapes, by tracing the characters on the species phylogenetic tree of Dioon. We were able to describe the leaflet anatomy, cuticles, and epidermal features for 14 Dioon species. The quantitative analysis was useful to reveal five geographically structured species groups. Character tracing on the phylogenetic tree of Dioon has amplified our current understanding on species relationships with respect to habitats. The presence/absence data suggest that the evolutionary acquisition-deletion of structural shapes is phylogenetically independent, thus climate seems to play a very important role in the variation of cuticular and stomatal traits. Many epidermal traits, especially adaxial cuticle thickness and epistomatal pore width and depth, might be adaptations resulting from a long-term influence of climate, since they appear to have correlation with climatic conditions in relation to their biogeography. We conclude that the variation of all traits are mostly sustained and intrinsic to the species, and are of promising taxonomic value. The combination of the epidermal traits with other characters has potential for taxonomic resolution at species level.
Biology Letters
The morphology of the early ontogenetic stages of cycad foliage may help resolve the relationships between extinct to extant cycad lineages. However, prior to this study, fossil evidence of cycad seedlings was not known. We describe a compression fossil of cycad eophylls with co-occurring fully developed leaves of adult specimens from the early Palaeocene ( ca 63.8 Ma) Castle Rock flora from the Denver Basin, CO, USA and assign it to the fossil genus Dioonopsis (Cycadales) based on leaf morphology and anatomy. The new fossil seedling foliage is particularly important because fully differentiated pinnate leaves of adult plants and the eophylls belong to the same species based on shared epidermal micromorphology, therefore, increasing the number of morphological characteristics that can be used to place Dioonopsis phylogenetically. Significantly, the seedling fossil has a basic foliage structure that is very similar to seedlings of extant cycads, which is consistent with a cycadalean ...
Leaf anatomy of a late Palaeozoic cycad
Biology letters, 2017
Today, cycads are a small group of gymnospermous plants with a limited distribution in the (sub)tropics, but they were major constituents of Mesozoic floras. Fossil leaves sporadically found in latest Carboniferous and Permian floras have putatively been ascribed to cycads. However, their true affinity remains unclear due to the lack of anatomical evidence. Virtually all modern cycads have pinnate leaves, but this type of leaf morphology is by no means unique for cycads. Pinnate leaves of Plagiozamites oblongifolius Halle 1927 with well-preserved cuticles showing the epidermal anatomy are here described from the upper Permian Xuanwei Formation of Yunnan Province, Southwest China. The cuticles show a clear differentiation into costal and intercostal zones; stomata are confined to the intercostal zones on both the upper and lower leaf surfaces. The external morphology and the epidermal anatomy of these fossil leaves are closely comparable with those of extant cycads, particularly memb...
Revista Mexicana de Biodiversidad, 2020
Based on their morphological traits and elevation distribution, we analyzed 15 populations of Dioon edule and D. angustifolium located in the Sierra Madre Oriental in an elevation gradient from 294 to 1,314 m asl, to identify the forms proposed by Whitelock (2004). A non-parametric test was applied to find differences among elevation and populations. A discriminant analysis was applied to classify the population forms and calculate the proportion of well-classified observations, as well as Maxent to select the environmental predictors of the population's distribution. Ten populations were grouped into 3 forms proposed by Whitelock (2004): "angustifolium", "edule" and "rioverde", but 5 populations could not be classified as proposed forms, and they were named "tamasopo". The forms "tamasopo" and "rioverde" present intermediate values between the 2 species, with 63% of the individuals classified as "tamasopo" an...
Macaronesia and eastern Africa-Arabia, referred to as the Rand flora biogeographic pattern, is the "dragon tree group" within Dracaena (Asparagaceae). However, little is known about the evolutionary origin of this iconic group of semi-desertic trees. Here, we use exceptionally well-preserved fossils from western Anatolia to demonstrate range and ecological shifts of the lineage probably leading to some of the modern dragon trees. Compression fossils of apical leaf rosettes and detached leaves of Dracaena tayfunii spec. nov. were compared to modern Dracaena using the architecture of leaf-bearing branches, leaf morphology, and highly diagnostic leaf epidermal features observed with light and electron scanning microscopy. The palaeoecology of Dracaena was inferred using the depositional setting and associated plant taxa. The ca. 16 million-year-old (Ma) Dracaena from western Anatolia shows a character combination restricted today to the Macaronesian dragon tree, Dracaena draco: (1) Leaves are arranged in terminal rosettes; (2) leaves are ensiform, oblong, with a conspicuously dilated base (pseudo-sheath); and (3) leaf epidermis is strongly papillate with sunken stomata overarched by papillae of four neighbouring epidermal cells. Depositional setting, taphonomy, and the fossil plant association indicate that the Miocene Dracaena either grew in seasonally dry swamps within a complex fluvial-lacustrine environment or on adjacent slopes under a humid, warm climate. Hence, semi-desertic modern dragon trees allied to D. draco displaying distinct xeromorphism may have originated from a western Eurasian mesic lineage that had evolved xeromorphic characteristics by the Miocene. The morphology of this mesic ancestor later enabled the lineage to colonize and survive in the semi-desertic environments where it is found today. The new fossil species of Dracaena represents a classic example of pre-adaptation and niche shift.
Botanical Journal of the Linnean Society, 2003
The relationship in geographical distribution and morphological variation of leaflet width and length (diagnostic trait), between and within populations of Dioon edule Lindl., has been investigated throughout its known range in eastern Mexico (from the states of Nuevo León to Veracruz, north to south, respectively). A total of 1832 leaflets were measured for width and length from 154 plants distributed amongst five populations using four leaflet replicas from each of three leaves per plant. For leaflet width and length the variation among populations indicated significant statistical differences ( F 4,147 = 125.83; P < 0.0001; R 2 = 92.17% and F 4,147 = 9.04; P < 0.001; R 2 = 26.8%), respectively. With respect to leaflet width, the multiple range test showed three groups with a north to south distributional relationship along the range of the species. The correlation coefficient among paired populations, respect to geographical distance and the absolute value of the mean difference of leaflet width in each population, was positive, and different from zero ( r = 0.82; P = 0.013). A great variation of important ecological and evolutionary parameters was shown.
2014
Among the most prominent examples for the disjunct distribution of xeromorphic-sclerophyllous plants in Macaronesia and eastern Africa–Arabia, referred to as the Rand flora biogeographic pattern, is the “dragon tree group” within Dracaena (Asparagaceae). However, little is known about the evolutionary origin of this iconic group of semi-desertic trees. Here, we use exceptionally well-preserved fossils from western Anatolia to demonstrate range and ecological shifts of the lineage probably leading to some of the modern dragon trees. Compression fossils of apical leaf rosettes and detached leaves of Dracaena tayfunii spec. nov. were compared to modern Dracaena using the architecture of leaf-bearing branches, leaf morphology, and highly diagnostic leaf epidermal features observed with light and electron scanning microscopy. The palaeoecology of Dracaena was inferred using the depositional setting and associated plant taxa. The ca. 16 million-year-old (Ma) Dracaena from western Anatolia shows a character combination restricted today to the Macaronesian dragon tree, Dracaena draco: (1) Leaves are arranged in terminal rosettes; (2) leaves are ensiform, oblong, with a conspicuously dilated base (pseudo-sheath); and (3) leaf epidermis is strongly papillate with sunken stomata overarched by papillae of four neighbouring epidermal cells. Depositional setting, taphonomy, and the fossil plant association indicate that the Miocene Dracaena either grew in seasonally dry swamps within a complex fluvial–lacustrine environment or on adjacent slopes under a humid, warm climate. Hence, semi-desertic modern dragon trees allied to D. draco displaying distinct xeromorphism may have originated from a western Eurasian mesic lineage that had evolved xeromorphic characteristics by the Miocene. The morphology of this mesic ancestor later enabled the lineage to colonize and survive in the semi-desertic environments where it is found today. The new fossil species of Dracaena represents a classic example of pre-adaptation and niche shift.
2017
Dicranophyllum gallicum Grand'Eury is described by means of a morphometric analysis of eighty two samples from various old and new localities in western and central Europe. Stem, leaf cushions, leaf scars, leaves, axillary structures and potential seeds are described in detail, and discussed in comparison to earlier studies. The encountered variability in size and structure is shown to be higher than what was described earlier. The organisation of the leaf cushion and scar density vary gradually with the stem width, while stratigraphic position and ecology do not relate to it. It is concluded that the described variability represents an ontogenetic feature rather than a phylogenetic or ecologic one. The juvenile plants are characterised by small stems, a high leaf scar density and elongated leaf cushions with a dominant apical field, while mature specimens are characterized by a wide stem, a relatively low leaf scar density and relatively wide leaf cushions with a pronounced basal field. Axillary shoots and potential seeds of D. gallicum are described and illustrated in detail for the first time. A reconstruction based on the studied material is presented.
2011
Five fossil species (Pseudocycas dunkeriana, Tsuga europaea, Taxodium dubium, Platanus neptuni and Juglans acuminata) have been compared to several present-day related species (Cycas revoluta, Tsuga canadensis, Taxodium distichum, Platanus hybrida and Juglans regia) on the basis of some leaf epidermal features: the size of the epidermal cells of the leaves and stomata, as well as their other characteristics. We focused on similarities and some differences that exist between fossil and present-day related species.