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Abstract Taxonomic data is essential to advance the discovery and description of biodiversity, as well as the study of evolutionary processes. Emerging large-scale datasets and new methods of analysis have provided different approaches to describe biodiversity. Here, we present a review of the taxonomic history in Cycadales including an analysis of historical taxonomic concepts and approaches used for species delimitation. We examine the trends in the publication of new species following taxonomic works in books, journals and horticultural catalogues, monographic projects and floras where species treatments were published. In addition, we review the studies concerning species delimitations using the literature available in scientific journals appearing in the database ISI Web of Knowledge. The approaches used were discussed throughout all research focused on empirical and theoretical considerations in each study. We review the current state of the studies on causal processes that have given rise to the currently recognized diversity. The trend shows that taxonomic work on discovery and description of species has been intensive in the last 40 years culminating in 38.8% of binomials published. As a result, we consider the relevance of the monographs and floras for identification of species for other biological disciplines and the content of these contributions is compared and discussed. A total of six criteria (diagnosability, phenetic, phylogenetic, genotypic cluster, niche specialization and coalescent) were detected from the following three approaches to species delimitation within Cycadales: traditional, integrative taxonomy, and monophyletic. In all cases, the results from these species delimitations not only provided a taxonomic treatment or proposed a new species, but also supposedly clarified the other species involved as a result of the new taxonomic concept of the new species described. Most investigations of species delimitation used the traditional approach or a phenetic criteria. Finally, we discuss evolutionary studies on causal processes involved in cycad diversity. This is considered in the context of species delimitation as hypothesis testing for a successful evaluation of variation in both genetic and morphological understanding. 

Premise of research: In our modern flora, the Cycadales represent one of the oldest-known gymnosperm clades, with their evolutionary roots tracing back to the late Paleozoic. Their radiation and wide distribution in the Mesozoic are well documented by numerous fossils. In contrast, the fossil record of late Paleozoic forms is restricted to a few specimens, thus leaving open questions on the origin and early evolution of cycads. A petrified stem with cycadalean affinity has been found in Saxony (central-eastern Germany) in Holocene gravel deposits of the Zwickauer Mulde river as a result of fluvial transportation from its original lower Permian locality. Methodology: The specimen was sectioned transversely, radially, and tangentially. Its provenance was clarified by comparing fossil woods of various localities in the upstream catchment area. Samples of these localities were exposed to ultraviolet light of different wavelengths, revealing distinctive fluorescence patterns related to specific geochemical conditions during the fossilization process. Plant anatomical studies were performed by macroscopic and microscopic documentation, including photo scanning, microscopic photography, and anatomical measurements. Pivotal results: Cycadodendron galtieri gen. nov. et sp. nov. originates from the Chemnitz Fossil Lagerstätte, an autochthonous floral assemblage of early Permian age (291 Ma; Sakmarian–Artinskian) that has been buried and conserved by pyroclastics in a geological instant. Several anatomical characteristics provide evidence for its cycadalean affinity: (1) a wide pith with numerous scattered medullary bundles, (2) a pith-peripheral vascular system with endarch primary xylem bundles, (3) at least nine successive vascular segments with secondary xylem and phloem, (4) araucarioid-type pitting of secondary xylem tracheids, and (5) primary rays and medullary bundles traversing the vascular segments. Conclusions: Cycadodendron galtieri gen. nov. et sp. nov. provides insights into stem anatomical characteristics of the oldest-known cycads, for example, revealing that polyxyly was an early-derived feature in cycad evolution. Its provenance reveals that the arborescent but generally small taxon was part of intramontane forested landscapes thriving on a well-drained mineral substrate in an alluvial plain setting and experiencing seasonally dry paleoclimate. 

Zamia magnifica (Zamiaceae), a new species endemic to Sierra Norte, Oaxaca, Mexico, is described. Zamia magnifica is characterized by having a rupicolous habit, pendent leaves bearing leaflets that are densely tomentose and pink to caramel in color when emerging, and broad oblong leaflets that are coriaceous in texture with few non-prominent denticulations and ovulate strobili with short (<4 cm) peduncles. It is compared to Z. furfuracea and Z. meermanii, the Mesoamerican Zamia species to which it shares the closest morphological resemblance. 

Zamia multidentata is described and illustrated here as a new species from the Amazon basin, state of Acre, Brazil. The new species shares morphological similarities with the Amazonian species Z. hymenophyllidia, and Z. urep, to which it is compared. The combination of slender (to 6.2 cm) caulescent stems, strongly serrulate elliptic leaflets with long acuminate tips and a pronounced adaxially raised longitudinal crease, as well as seed strobili with long peduncles (15 cm +) and flat megasporophylls distinguish the new species Zamia multidentata from all other known species in the genus. 

Ceratozamia Brongn. is one of the species-rich genera of Cycadales comprising 38 species that are mainly distributed in Mexico, with a few species reported from neighboring regions. Phylogenetic relationships within the genus need detailed investigation based on extensive datasets and reliable systematic approaches. Therefore, we used 30 of the known 38 species to reconstruct the phylogeny based on transcriptome data of 3954 single-copy nuclear genes (SCGs) via coalescent and concatenated approaches and three comparative datasets (nt/nt12/aa). Based on all these methods, Ceratozamia is divided into six phylogenetic subclades within three major clades. There were a few discrepancies regarding phylogenetic position of some species within these subclades. Using these phylogenetic trees, biogeographic history and morphological diversity of the genus are explored. Ceratozamia originated from ancestors in southern Mexico since the mid-Miocene. There is a distinct distribution pattern of species through the Trans-Mexican Volcanic Belt (TMVB), that act as a barrier for the species dispersal at TMVB and its southern and northern part. Limited dispersal events occurred during the late Miocene, and maximum diversification happened during the Pliocene epoch. Our study provides a new insight into phylogenetic relationships, the origin and dispersal routes, and morphological diversity of the genus Ceratozamia. We also explain how past climatic changes affected the diversification of this Mesoamerica-native genus. 

Ceratozamia (Zamiaceae, Cycadales), is a member one of the most endangered seed plant groups. Species of Ceratozamia grow from near sea level up to 2,100 meters in Mexico and Mesoamerica. We present a modern taxonomic treatment of Ceratozamia , based on fieldwork combined with detailed study of herbarium specimens in and from Mexico and Central America. This new revision is based on incorporation of morphological, molecular and biogeographic data that have been previously published in circumscriptions of species complexes by our group. Detailed morphological descriptions of the 36 species of Ceratozamia are provided and relevant characters for the genus are discussed and described. A majority are endemic to Mexico and are concentrated at high elevations in mountainous areas. Synonymies, lectotypifications, etymologies, taxonomic notes, distribution maps, illustrations and detailed species-level comparisons are included, as well as a dichotomous key for identification of all species. Data on distributional ranges and habitats of all species are summarized. Ceratozamia osbornei D.W.Stev., Mart.-Domínguez & Nic.-Mor., sp. nov. is described from evergreen tropical forests of Belize and we highlight new populations and distributional ranges for C. subroseophylla Mart.-Domínguez & Nic.-Mor. and C. vovidesii Pérez-Farr. & Iglesias in the Mesoamerican region. 

Abstract Background and Aims Cycads are regarded as an ancient lineage of living seed plants, and hold important clues to understand the early evolutionary trends of seed plants. The molecular phylogeny and spatio-temporal diversification of one of the species-rich genera of cycads, Macrozamia, have not been well reconstructed. Methods We analysed a transcriptome dataset of 4740 single-copy nuclear genes (SCGs) of 39 Macrozamia species and two outgroup taxa. Based on concatenated (maximum parsimony, maximum likelihood) and multispecies coalescent analyses, we first establish a well-resolved phylogenetic tree of Macrozamia. To identify cyto-nuclear incongruence, the plastid protein coding genes (PCGs) from transcriptome data are extracted using the software HybPiper. Furthermore, we explore the biogeographical history of the genus and shed light on the pattern of floristic exchange between three distinct areas of Australia. Six key diagnostic characters are traced on the phylogenetic framework using two comparative methods, and infra-generic classification is investigated. Key Results The tree topologies of concatenated and multi-species coalescent analyses of SCGs are mostly congruent with a few conflicting nodes, while those from plastid PCGs show poorly supported relationships. The genus contains three major clades that correspond to their distinct distributional areas in Australia. The crown group of Macrozamia is estimated to around 11.80 Ma, with a major expansion in the last 5–6 Myr. Six morphological characters show homoplasy, and the traditional phenetic sectional division of the genus is inconsistent with this current phylogeny. Conclusions This first detailed phylogenetic investigation of Macrozamia demonstrates promising prospects of SCGs in resolving phylogenetic relationships within cycads. Our study suggests that Macrozamia, once widely distributed in Australia, underwent major extinctions because of fluctuating climatic conditions such as cooling and mesic biome disappearance in the past. The current close placement of morphologically distinct species in the phylogenetic tree may be related to neotenic events that occurred in the genus.