Botanical Journal of the Linnean Society

Terrones, Alejandro; Juan, Ana

doi: 10.1093/botlinnean/boad025pmid: N/A

The genus Tamarix comprises trees and shrubs that grow mainly in saline habitats. Previous phylogenetic analyses have shown incongruence between different gene trees, which suggest that hybridization processes might have been present in the past. However, the complex pattern of colonization of the Western Mediterranean region has yet to be understood, and no dated phylogeny that reconciles the different gene trees is currently available. The objectives of the study are: (i) to reconstruct the first dated species tree of the genus Tamarix from previously published data, (ii) to evaluate the occurrence of past hybridization, and (iii) to discuss biogeographical implications, mainly focused on the Mediterranean Basin. Our results show that the separation between Tamarix and Myricaria occurred 28.49 Mya, and the crown age of the genus Tamarix is dated at 16.65 Mya. Past hybridization processes might be present in three species: Tamarix amplexicaulis, Tamarix canariensis, and Tamarix minoa. Various colonization events are probable in the Western Mediterranean: a first colonization in the Early Miocene, Tamarix africana during the Late Miocene, and Tamarix boveana and Tamarix gallica during the Pleistocene. In addition, the genus Tamarix migrated to south-western Africa around 5.8 Mya, probably through an ancient arid African corridor, or a long-distance dispersal event.

Freire-Fierro, Alina; Forest, Felix; Devey, Dion S; Pastore, José Floriano Barea; Horn, James W; Ge, Xue-Jun; Wang, Zhengyang; Xiao, Tian-Wen; Bien, Walter F

doi: 10.1093/botlinnean/boad026pmid: N/A

Endemic to the Neotropics, Monnina is the second largest genus of Polygalaceae, yet little is known about its phylogenetic history, biogeography, and morphological character evolution. To address these knowledge gaps, we conducted Bayesian and maximum likelihood (ML) analyses of nuclear ITS and plastid trnL–F regions to test the monophyly of Monnina s.l. We used this phylogenetic framework to (i) infer divergence time estimates of lineages within the genus and reconstruct their historical biogeography; (ii) reconstruct the evolution of morphological characters of putative ecological and evolutionary importance in Monnina; and (iii) test for correlations between our phylogenetic hypothesis and environmental data. Our results reveal that Monnina is monophyletic with an indehiscent, 1–2-seeded fruit as a synapomorphy for the genus. We identify six clades within Monnina based on our combined phylogenetic results: Clades A, B, and D are primarily distributed in southern and eastern South America, Clades C and E are primarily Central Andean, and Clade F is chiefly distributed in the Northern Andes and Central America. The ancestor of the Monnina stem lineage dispersed from Australia/Africa to South America during the late Eocene to early Oligocene. The divergences of major lineages within the genus began in the early Miocene. We inferred the most recent common ancestor of Monnina to be an herbaceous plant with one-seeded samaroid fruits. The origins of fleshy fruits and shrubby habits are phylogenetically correlated within Monnina, and their concerted convergent evolution may have promoted increased net diversification rates in the two most species-rich subclades of the genus.

Nuñez-Florentin, Mariela; Verstraete, Brecht; Salas, Roberto M; Dessein, Steven

doi: 10.1093/botlinnean/boad023pmid: N/A

The orbicules are tiny structures of sporopollenin that occur on the interior wall of anthers in several groups of plants, and they are associated with pollen grains and tapetal cells. Although their function remains still unresolved, they have been widely used in systematics. Rubiaceae is one of the most studied families in this aspect. However, scarce information is available about the orbicules in the tribe Spermacoceae, especially in the Spermacoce clade. The main objectives of this work were to investigate the occurrence, general morphology, evolution, and systematic utility of the orbicular characters in the Spermacoce clade. We investigated the presence/absence, size, abundance, shape, and ornamentation of orbicules in 104 specimens from 84 species in the Spermacoce clade using scanning electron microscopy (SEM). On the basis of these features, the ancestral state reconstruction analyses were performed on a custom-made phylogeny by stochastic character mapping. The orbicules are present in 38 (44%) of 84 analysed species, corresponding to 13 genera (56%) of the Spermacoce clade. Seven genera have orbicules in all analysed species, eight genera lack orbicules in all analysed species, and six genera show both presence and absence of orbicules. The absence of orbicules was estimated to be the ancestral state for the Spermacoce clade and the presence of orbicules evolved several times independently within Clade B. The absence of orbicules in the common ancestor of the Spermacoce clade can be seen as one of the independent losses that occurred during the evolutionary history of the Rubiaceae.

Silva, Lucimara Reis de Oliveira; Trevisan, Rafael; Oriani, Aline

doi: 10.1093/botlinnean/boad029pmid: N/A

Species of Cyperoideae exhibit wide morphological variation in their flowers due to reduction processes. Their flowers can be bisexual or unisexual, achlamydeous or not, with tepals and stamens varying from one to six and a trimerous or dimerous gynoecium, the latter dorsiventrally or laterally flattened. We studied the floral anatomy and vasculature of Fuirena robusta, Cyperus sesquiflorus, Rhynchospora panicoides, and Schoenoplectus californicus to understand the reduction processes that resulted in different floral morphologies. The floral development of C. sesquiflorus was also analysed. All these species have spikelets with bisexual flowers, but they vary in relation to the perianth, androecium, and gynoecium. Our results show the loss of the outer abaxial tepal in R. panicoides, the total loss of the outer whorl of tepals in F. robusta, and the loss of abaxial tepals (outer and inner) in S. californicus. The tepals are vascularized in F. robusta and R. panicoides and non-vascularized in S. californicus. In C. sesquiflorus, the perianth is absent. Phenolic compounds present in the epidermal cells of the receptacle mark the boundaries between tepals and stamens, before the individualization of these parts. The three stamens present in F. robusta and R. panicoides correspond to the outer whorl. In S. californicus, there is a loss of the adaxial stamens (outer and inner), whereas in C. sesquiflorus the outer stamen whorl and the inner adaxial stamen are lost. The laterally flattened dimerous gynoecium in C. sesquiflorus may be the result of the pressure exerted by the distichously arranged glumes. The most distal flower of the spikelet in this species is staminate by abortion of the gynoecium. The morphological diversity observed in the flowers of Cyperoideae is the result of distinct reduction processes that probably occurred independently in the different clades of the subfamily during the evolution of Cyperaceae.

Couto, Maria Alice M S; Teixeira, Marcelo C; Gope, Alexia; Backes, Alice; Rodrigues, Daniele M; Soares, Geraldo L G; Turchetto, Caroline

doi: 10.1093/botlinnean/boad021pmid: N/A

Floral traits are used as signals to attract pollinators and play an important role in species identification and isolation. Nicotiana is a genus with a diverse range of flower morphologies, colours, and pollination systems related to a natural history of hybridization, a driver of speciation in this genus. Nicotiana alata and Nicotiana forgetiana are pollinated by hawkmoths and hummingbirds, respectively, and a putative hybrid population was recently found. This population presents flowers with intermediate phenotypes providing an opportunity to investigate the impact of hybridization on floral trait variation. Here we investigated the floral shape, floral pigments, and nectar traits in a putative hybrid population, hereafter termed atypical populations (AP) compared to phenotypes of allopatric populations of both species. We found a high variation in floral pigmentation in AP plants and observed phenotype segregation in some genotypes. Nicotiana forgetiana and AP plants showed the same flavanol peaks as Nicotiana alata, suggesting the same UV-absorbent phenotype attractive to hawkmoths. The geometric morphometric results showed that the intermediate-coloured flowers had similar floral shape and size to N. alata. Our results suggest that the putative hybrid population would be able to attract the same parental pollinator—hawkmoths and hummingbirds—making backcrossing events possible and attracting other pollinators, such as bees.

D’Antonio, Michael P

doi: 10.1093/botlinnean/boad028pmid: N/A

It is thought that arborescent lycopsid cambial expansion kept pace with radial wood growth via tangential broadening of the fusiform initials, resulting in progressive outward expansion in tracheid diameters and an absence of de novo tracheid files. This pattern appears in distal lycopsid axes but has not been investigated in proximal-most trunk vasculature where wood was thickest and primary xylem thinnest. Here, a ground-level trunk vasculature fossil of Sigillaria approximata in transverse section is described. This proximal vasculature diverges from the expectations of the current lycopsid wood production model in two main ways: first, inner and outer wood tracheids have approximately the same lumen diameters, such that there is no trend towards centrifugally increasing lumen diameters; and second, de novo cell files commonly appear within the wood. The outwards rate of cambial circumference expansion closely tracks the outwards rate of new wood tracheid file appearance, suggesting that the addition of new files is the primary way the cambium expanded proximally. Because this vasculature can only be studied in transverse section, the developmental mode producing new files cannot be determined. However, evidence from this specimen is sufficient to demonstrate that arborescent lycopsid wood production was more complex than previously understood.