We describe Oplonia doceana sp. nov. (Acanthaceae), a new species endemic to the campos rupestres of the João Pinto Formation in the Doce River basin, within the Atlantic Forest domain of southeastern Brazil. This is the first confirmed record of Oplonia in Brazil, extending the genus beyond its previously known range in Argentina, Bolivia, Peru, the West Indies, and Madagascar. Phylogenetic analysis based on plastid and nuclear regions supports its placement within Oplonia, where it is recovered as sister to O. jujuyensis, native to Argentina and Bolivia. Morphologically, the species differs by its erect habit, chartaceous leaves with domatia, red infundibular corolla, and unusual terminal inflorescences, which contrast with the axillary inflorescences typical of Oplonia. These traits suggest a potential pollination shift and highlight challenges in Graptophyllinae taxonomy, where generic boundaries remain unclear. Oplonia doceana is currently known from only a few locations and specialized habitats facing multiple threats, including fire, invasive species, and ongoing habitat disturbance, qualifying it as Endangered under IUCN criteria. This discovery adds to a growing list of narrowly endemic angiosperms in the region and emphasizes the João Pinto Formation as a hotspot of botanical novelty and conservation priority within the Atlantic Forest domain, underscoring the urgent need for continued taxonomic research and targeted conservation in the Doce River basin.

The Acanthaceae tribe Barlerieae is an understudied lineage that consists of ca. 500 species, many of which are rare and range restricted. Though understudied, it is clear that many species play vital roles in tropical ecosystems, including supporting a wide range of pollinators and herbivores. The tribe contains 13 genera, the two largest and most widespread of which are the primarily Paleotropical Barleria (ca. 300 spp.) and pantropical Lepidagathis (ca. 150 spp.). In a recent reclassification of Acanthaceae, three subtribes were informally proposed based on corolla and calyx characters: (1) Barleria, (2) Crabbea and allies, and (3) Lepidagathis and allies. Using a next-generation sequencing approach, double-digest restriction associated DNA sequencing (ddRADseq), this study estimates a well-sampled phylogeny of the Barlerieae tribe, tests genera and infrageneric groups for monophyly, and identifies morphological characters that support monophyletic groups. Our study reveals strong support for the monophyly of Barlerieae and resolves relationships among all 13 genera currently recognized in the tribe. There is strong support for the three proposed subtribes. Our results also suggest that taxonomic revision of Lepidagathis is necessary. Species of Lepidagathis are found in three clades: (A) Lepidagathis s.str., (B) Lophostachys s.l., and (C) Teliostachya, each of which can be distinguished by inflorescence and stamen characters. The phylogenetic relationships recovered here indicate that each of the three clades should be classified as a separate genus. This research lays the groundwork for future taxonomic revisionary work as well as the construction of updated identification keys that will aid in conservation efforts and provide insight into the evolutionary processes that shape biodiversity in this remarkable lineage.

The new genus Cryptacanthus I.Darbysh. Kiel (Acanthaceae: Acanthoideae: Justicieae: Justiciinae) is described from the Guineo-Congolian forests of West and Central Africa based on a combination of molecular phylogenetic data and macro- and micro-morphological studies. Previously referred to informally as the “Rhinacanthus virens Clade”, it comprises three species currently placed in either Justicia L. or Rhinacanthus Nees, namely J. tenuipes S.Moore, R. obtusifolius (Heine) I.Darbysh. and R. virens (Nees) Milne-Redh. for which new combinations are made, plus three species endemic to Cameroon, all of which are newly described here, namely Cryptacanthus bakossii I.Darbysh., C. ebo Cheek and C. obovatus I.Darbysh. With the exception of the widespread R. virens, for which recent accounts already exist, descriptions and illustrations are provided for all of the species, and notes on their habitat preferences, distribution and extinction risk status are provided. The new species are all considered to be Critically Endangered based upon current evidence.

BACKGROUND AND AIMS:Few studies of angiosperms have focused on androecial evolution in conjunction with evolutionary shifts in corolla morphology and pollinator relationships. The Western Hemisphere clade of Justiciinae (Acanthaceae) presents the rare opportunity to examine remarkable diversity in staminal morphology. We took a phylogenetically informed approach to examine staminal diversity in this hypervariable group and asked whether differences in anther thecae separation is associated with phylogenetically informed patterns of variation in corolla morphology. We further discuss evidence for associations between anther diversity and pollinators in this lineage. METHODS:For the Dianthera/Sarotheca/Plagiacanthus (DSP) clade of Western Hemisphere Justiciinae, we characterized floral diversity based on a series of corolla measurements and using a model-based clustering approach. We then tested for correlations between anther thecae separation and corolla traits, and for shifts in trait evolution, including evidence for convergence. KEY RESULTS:There is evolutionary vagility in corolla and anther traits across the DSP clade with little signal of phylogenetic constraint. Floral morphology clusters into four distinct groups that are, in turn, strongly associated with anther thecae separation, a novel result in Acanthaceae and, to our knowledge, across flowering plants. These cluster groups are marked by floral traits that strongly point to associations with pollinating animals. Specifically, species that are known or likely to be hummingbird pollinated have stamens with parallel thecae, whereas those that are likely bee or fly pollinated have stamens with offset, divergent thecae. CONCLUSIONS:Our results suggest that anther thecae separation is likely under selection in concert with other corolla characters. Significant morphological shifts detected by our analyses corresponded to putative shifts from insect to hummingbird pollination. Results from this study support the hypothesis that floral structures function in an integrated manner and are likely subject to selection as a suite. Further, these changes can be hypothesized to represent adaptive evolution.

Summary Current generic delimitation in subtribe Isoglossinae of Acanthaceae is discussed using available morphological and molecular data. Particular consideration is given to the small genera endemic to Madagascar — Celerina Benoist, Melittacanthus S.Moore, Sphacanthus Benoist and the illegitimate Conocalyx Benoist — and how these relate to the current circumscription of Isoglossa Oerst. The relative merits and challenges of recognising a broadly circumscribed Isoglossa are considered. Isoglossa s.l. is readily recognisable by combining a bilabiate corolla, with an androecium comprising two bithecous stamens and lacking staminodes, and with the presence of gürtelpollen (i.e. bipororate pollen, circular in apertural view and with a pronounced interapertural “girdle” of tectate exine), whilst the segregate genera as currently defined are not separable morphologically. However, the limited molecular phylogenetic data available to date indicate that Isoglossa s.l. is paraphyletic. Pending further molecular studies of this group to clarify generic delimitation, it is proposed that all new taxa in bithecous Isoglossinae should be described in Isoglossa as an interim solution . Four new species of Isoglossa are described: I. eburnea Onjalal. & I.Darbysh., I. pterocalyx I.Darbysh. & Phillipson, I. pseudoanisotes I.Darbysh. and I. conocalyx I.Darbysh. & Callm., the lattermost of which is based on Conocalyx laxus Benoist nom. illegit. In addition, Justicia onilahensis Benoist (including Ritonia poissonii Benoist) and Anisotes perplexus T.F.Daniel, Letsara & Martín-Bravo are transferred to Isoglossa , and three names within Justicia L. are synonymised within existing taxa in Isoglossinae. Lectotypes are selected for Sphacanthus brillantaisia Benoist, S. humbertii Benoist and Justicia subpaniculata Benoist (= Celerina seyrigii Benoist var. egena Benoist).

Acanthaceae is a family of tropical flowering plants with approximately 4900 species. Despite remarkable variation in morphological traits, research on patterns of character evolution has been limited by uncertain relationships among some of the major lineages. We sampled 16 taxa from these major lineages to estimate a phylogenomic framework using a combination of five newly sequenced shotgun genome skims plus seven new and four publicly available transcriptomes. We used OrthoFinder2 to infer a species tree with strong branch support. Except for the placement of Crabbea, our results corroborate the most recent chloroplast and nrITS sequence-based topology. Of 587 single copy loci, 10 were recovered for all 16 species; a RAxML tree estimated from these 10 loci resulted in the same topology as other datasets assembled in this study, with the exception of relationships among three sampled species of Barleria; however, branch support was lower compared to the tree reconstructed using more data. ABBA-BABA tests were conducted to investigate patterns of introgression involving Crabbea; few nucleotides supported alternative topologies. SplitsTree networks of the 587 loci and 6136 orthogroup trees revealed conflict among the branches leading to Andrographideae, Whitfieldieae, and Neuracanthus. A principal components analysis in treespace found no distinct clusters of trees. Our results based on combined genome skim and transcriptome sequences strongly corroborate the previously published chloroplast and nr-ITS-based phylogeny of Acanthaceae with increased resolution among Barlerieae, Andrographideae, Whitfieldieae, and Neuracanthus. This advance in our knowledge of Acanthaceae relationships will allow us to investigate character evolution and other phenomena within this diverse group of plants in studies with increased taxon sampling.

Acanthaceae are among the most taxonomically diverse, geographically widespread, and morphologically and ecologically variable lineages of flowering plants. Most modern workers have estimated more than 4000 species and potentially more than 5000 species worldwide, thus placing Acanthaceae among the 12 or so most diverse families of angiosperms. This diversity is marked by exceptional morphological variation, particularly with respect to floral forms, growth forms, and pollen types. The present work represents a synthesis of knowledge generated over the past two decades on the taxonomy and systematics of this complex plant family. We place all 191 accepted genera within a revised classification of the family. Dichotomous keys (nine in total) to recognize the major lineages of Acanthaceae are presented together with geographically partitioned keys to all genera, covering (a) Africa, Madagascar, the Mediterranean region, and Arabia; (b) Asia and Australasia; and (c) the Americas. Finally, we validate several new tribes, subtribes, and genera, and provide new combinations for species where generic delimitation has changed. Our hope is that the present contribution serves to benefit future research on the systematics of Acanthaceae and provides a foundation upon which future classification efforts can be built.

Barleria is a genus of approximately 300 species of herbs, shrubs or, rarely, trees, that is broadly distributed across the Paleotropics. The genus is especially diverse in Tanzania, Angola, and Madagascar. A recent molecular study sampled 53 Barleria species and gathered data for five molecular markers (i.e., four chloroplast loci and the nuclear nrITS) to find support for the recognition of two subgenera previously circumscribed based on morphology, subg. Barleria and subg. Prionitis. That study further reconstructed four previously recognized sections (i.e., Fissimura, Prionitis, Somalia, Stellatohirta) as monophyletic, while three others (i.e., Barleria, Cavirostrata, Chrysothrix) were recovered as para- or polyphyletic. The present study aimed to reconstruct phylogenetic relationships within Barleria based on a broader sample of taxa and many more characters. We sampled 190 accessions representing 184 taxa, including varieties and subspecies. The dataset includes 167 of the ca. 300 species currently recognized or about 56% of total species diversity. We relied heavily on herbarium specimens to sample across the taxonomic breadth and geographic range of Barleria. Single nucleotide polymorphism data were generated using double-digest restriction-site associated DNA sequencing (ddRADseq). The maximum likelihood phylogeny corroborated the topology estimated from the chloroplast and nrITS data, but with greatly increased resolution and support for fine-scale relationships. A coalescent analysis failed to resolve distant evolutionary relationships across Barleria and between Barleria and outgroups, but recovered the same or similar topologies within each Barleria section. Importantly, the ddRADseq phylogeny recovered seven major lineages within subg. Barleria and resolved a polytomy that included B. cristata, the type species of the genus. The topology suggests at least four independent dispersal events to Madagascar followed by three subsequent radiations. Our results broadly inform our understanding of diversity and evolution in one of the largest genera of Acanthaceae, representing an important step towards a stable subgeneric classification for the genus.

Recent molecular phylogenetic results have demonstrated that Monechma s.l., a group of plants with ecological importance in the savanna and succulent biomes of sub-Saharan Africa, is polyphyletic with two discrete lineages recognisable. In the present work, we recognise Monechma Groups I and II at the generic rank, which can be distinguished by differences in inflorescence characteristics and seed morphology. The nomenclatural implications of these findings are investigated. The lectotype of Monechma, M. bracteatum Hochst., is a part of a small lineage of plants closely allied to Justicia L. sect. Harnieria (Solms) Benth. for which the earliest valid name is found to be Meiosperma Raf. Hence, Monechma is synonymised within Meiosperma, which comprises six accepted species and two undescribed taxa. The majority of species of former Monechma s.l. are resolved within the second lineage for which the only validly published generic name is Pogonospermum Hochst. This resurrected genus comprises 34 accepted species plus two undescribed taxa. Pogonospermum displays considerable morphological variation and is here subdivided into six sections based primarily on differences in plant habit, inflorescence form, calyx, bract and bracteole venation, and seed indumentum. The new combinations and new sections are validated, and seven accepted species names are lectotypified.

We present phylogenetic results for Justicieae, the largest of the major lineages of Acanthaceae. With 300% more sequence data and a similarly increased but also more geographically representative taxon sample compared to the only previous study of the lineage as a whole, we confirm the existence of the Pseuderanthemum Lineage, Isoglossinae, the Tetramerium Lineage and the Justicioid Lineage. To the last three lineages, we add a number of taxa with the goal of advancing our knowledge of genera (e.g., Isoglossa, Rhinacanthus) and of geographic areas (e.g., Malagasy and Asian Acanthaceae). These added taxa are accommodated within the phylogenetic framework for the lineages established in our earlier work with one exception. The monospecific genus Ichthyostoma is not placed in any of the established lineages but is instead sister to (Tetramerium Lineage + Justicioid Lineage). As this result is unexpected, we examined topologies both including and excluding this plant which revealed that other aspects of relationships remain stable whether Ichthyostoma is included or not. We point to Ichthyostoma as one of several Justicieae that will benefit from additional study. One species of Isoglossa is placed in the Tetramerium Lineage instead of with all other sampled members of the genus in Isoglossinae. Pollen morphology of I. variegata is more consistent with its phylogenetic placement here than with its taxonomic assignment to Isoglossa. As suggested in our earlier work, pollen morphology can be a powerful signal of phylogenetic relationships in Justicieae. With our increased sampling, we show that the Ptyssiglottis Lineage, a relatively small group of African and Asian plants, warrants recognition separate from Isoglossinae. With the addition of the Ptyssiglottis Lineage and excluding Ichthyostoma for now, the lineages of Justicieae are related as follows: (Pseuderanthemum Lineage ((Isoglossinae + Ptyssiglottis Lineage) (Tetramerium Lineage + Justicioid Lineage))). The Pseuderanthemum Lineage has been understudied to date and we here attempt to include representatives of all genera that are putatively part of this lineage and also to test monophyly of the larger genera. We identify a number of strongly supported clades but some aspects of relationship remain unresolved. Asystasia, Graptophyllum, Oplonia, and Pseuderanthemum are not monophyletic although, with a small number of nomenclatural changes, the first and second can be rendered monophyletic. With a range essentially as extensive as that of Justicieae as a whole, the Pseuderanthemum Lineage is biogeographically complex with patterns of distribution suggestive of multiple shifts between continents including Australia and parts of the Pacific basin. The calibrated phylogeny confirms that intercontinental shifts in distribution across Justicieae must have been by long-distance dispersal rather than by vicariance or stepwise dispersal over land bridges and also points to a number of groups that have potentially undergone rapid diversification. The Pseuderanthemum Lineage, in particular, requires considerable additional research to both understand relationships and achieve an informative taxonomy for the group. Although we here establish a phylogenetic framework across Justicieae, Next Generation Sequence data will be necessary to elucidate details of relationships in most lineages. Additional study of structural characters is also warranted as we continue to be unable to identify structural synapomorphies for a number of aspects of phylogenetic relationships that are very strongly supported by molecular data.

Abstract A species previously treated in Staurogyne (S. nitida) is elevated to the category of a new genus of Acanthaceae, subfamily Nelsonioideae, based on morphological and molecular data. The sole species, Aymoreana nitida, occurs in the Atlantic Forest of eastern Brazil, from southern Bahia to northern Espírito Santo. Aymoreana differs from other genera of Nelsonioideae by the combination of the calyx with subequal segments, the slightly zygomorphic corolla, the four didynamous stamens, and the asymmetric gynoecium. Morphological information is accompanied by a molecular phylogenetic tree, ecological data, a preliminary conservation assessment, and illustrations.

Monechma Hochst. s.l. (Acanthaceae) is a diverse and ecologically important plant group in sub-Saharan Africa, well represented in the fire-prone savanna biome and with a striking radiation into the non-fire-prone succulent biome in the Namib Desert. We used RADseq to reconstruct evolutionary relationships within Monechma s.l. and found it to be non-monophyletic and composed of two distinct clades: Group I comprises eight species resolved within the Harnieria clade, whilst Group II comprises 35 species related to the Diclipterinae clade. Our analyses suggest the common ancestors of both clades of Monechma occupied savannas, but both of these radiations (~13 mya crown ages) pre-date the currently accepted origin of the savanna biome in Africa, 5–10 mya. Diversification in the succulent biome of the Namib Desert is dated as beginning only ~1.9 mya. Inflorescence and seed morphology are found to distinguish Groups I and II and related taxa in the Justicioid lineage. Monechma Group II is morphologically diverse, with variation in some traits related to ecological diversification including plant habit. The present work enables future research on these important lineages and provides evidence towards understanding the biogeographical history of continental Africa.

Barleria is a genus of ~300 species of herbs and shrubs in Africa and Asia, with highest diversity in tropical East Africa and southern Africa. The genus is part of Barlerieae (Acanthaceae), a lineage that is distinguished from other Acanthaceae by quincuncial corolla aestivation. Unequivocal synapomorphies have yet to be identified for Barleria. However, among Barlerieae, species of Barleria can be recognized by the combination of 4‐partite calyces with the anterior and posterior lobes usually larger than the two lateral lobes, pollen with a coarsely reticulate (honeycomb) exine and the corolla limb variously subactinomorphic to strongly zygomorphic but never markedly bilabiate with a hooded upper lip. All Barleria that we have observed also have filaments that twist through 180° and cross just distal to the synstapetal zone. Barleria species have previously been classified into two subgenera and seven sections based on differences in leaf axil spine systems; configuration of the corolla, androecium and stigma; and morphology of the capsule and seed. We tested the subgeneric classification of Barleria by sampling 53 Barleria species and 9 outgroup species for three plastid intergenic spacers (trnS‐G, ndhF‐rpl32‐trnL(UAG)) and the nuclear region nrITS. We found a monophyletic Barleria and support for the two currently recognized subgenera; four of seven currently recognized sections are monophyletic but one of these four, sect. Fissimura, is nested within other sections. Species of sect. Fissimura unexpectedly resolved in subg. Barleria with strong support, although previous classifications placed the section in subg. Prionitis. We propose recognizing two subgenera (i.e., Barleria, Prionitis), the latter comprising three sections (i.e., Prionitis, Somalia, Stellatohirta). Barleria encompasses remarkable morphological diversity; we used an ultrametric tree to examine the evolution of nine morphological traits used to define infrageneric taxa in previous classifications. All characters evolved homoplasiously, but a few states (e.g., woody capsule septa) are supported as synapomorphies, and combinations of characters can be used to delimit subgenera. Members of subg. Barleria have 4‐seeded capsules that lack a prominent beak, with a transition to 2‐seeded capsules in the clade that corresponds to sect. Fissimura. In contrast, members of subg. Prionitis have 2‐seeded capsules (reversed to 4‐seeded in most members of one clade of sect. Somalia) that generally have a prominent beak. Additionally, we surveyed pollen morphology for 15 species sampled from across the classification. Pollen is consistently tricolporate with a coarse honeycomb exine. We provide an infrageneric classification and key to infrageneric taxa of Barleria.

Summary DNA sequence data, macro-morphological evidence and pollen analysis are used to clarify the phylogenetic placement of two African species of Acanthaceae: Schaueria populifolia C.B.Clarke and Rhinacanthus ndorensis Schweinf. The combined data demonstrate that these species are only distantly related to the genera in which they are currently placed and provide strong support for recognition of new genera to accommodate them. Two new genera are therefore proposed and a taxonomic account is provided for each of these. The first, Champluviera I.Darbysh., T.F.Daniel & C.A.Kiel, is based primarily on S. populifolia but Chlamydocardia nuda C.B.Clarke (= Justicia tigrina Heine) is also included within this new genus based on shared morphological traits, at least one of which is synapomorphic and restricted to these species. Based on molecular evidence, Champluviera is placed in a well-supported clade of several genera that are together sister to the core Isoglossinae lineage of tribe Justicieae. The genus may be recognised morphologically by the combination of a dense spiciform terminal thyrse with the bracts, bracteoles and calyx lobes all slender and closely resembling one another; a bilabiate corolla lacking a rugula and with intricate speckling or striping on the lips; and, in particular, the putatively synapomorphic trait of anther thecae with broad, flattened, basal appendages that have an irregularly toothed fringe. The second new genus, Kenyacanthus I.Darbysh. & C.A.Kiel, is based on R. ndorensis and is so far thought to be monospecific. It is placed between core Diclipterinae and Monechma Group II within the expanded subtribe Diclipterinae in tribe Justicieae. Kenyacanthus can be recognised morphologically by having the combination of a trailing or procumbent habit; fasciculate inflorescences; bracts, bracteoles and calyces with hyaline margins; a bilabiate corolla with a slender cylindrical tube longer than the limb and with a shallow rugula; stenotribic flowers, with the stamens held against the lower lip; and anthers with only slightly offset thecae that lack appendages.

Molecular data confirm monophyly of the Tetramerium lineage (Acanthaceae, Justicieae), a group of nearly 200 species, ca. 75% from the New World (NW) and the remainder from Asia or Africa. Compared to our earlier work, > 50% more in-group taxa were sampled (nearly 2/3 of known taxa now sampled) and added similar to 20% more sequence data. We time-calibrate the phylogeny using primary fossil evidence and the larger context of a calibrated phylogeny for Acanthaceae. Marty aspects of relationship are strongly supported but uncertainty remains about a number of phylogenetically isolated taxa (e.g. African Angkalanthus, Chorisochora; NW Ancistranthus) and some aspects of relationships among clades remain weakly supported. The group originated in the Old World (OW) and began diversifying about 11.5 Ma. A single dispersal event to the NW occurred about 8.3 Ma, likely from Africa to southwestern North America. A number of major clades, particularly in the NW, are less than 5 Ma old and species in many clades are substantially younger. Several NW clades, even those with < 10 species, comprise species that are markedly heterogeneous in floral traits likely reflecting selection by pollinators. Many NW genera are not monophyletic, which is not surprising given that floral traits have been relied upon taxonomically. Diversification rate analysis revealed no significant shifts resulting in a gradual increase in number of lineages with time. The Tetramerium lineage is now phylogenetically well characterized but remains enigmatic from the perspective of morphological evidence for many aspects of relationships. The lineage is usefully thought of as a 'clade complex': as a species complex is of morphologically confusing species, a 'clade complex' is of clades that are not well characterized morphologically.

In preparation for the publication of the Manual de Plantas de Costa Rica, new species, names, combinations, and synonymies are provided in six genera of Acanthaceae: Anisacanthus, Chamaeranthemum, Dicliptera, Justicia, Ruellia and Stenostephanus. The new species are A. grace-woodiae, J. altior, J. lithophila and S. chavesii. A new name at the species level, R. leonardiana, is provided for R. tubiflora var. hirsuta. With Habracanthus, Hansteinia, Kalbreyeriella and Razisea being subsumed within Stenostephanus, the new combinations S. blepharorhachis, S. citrinus, S. leiorhachis (= Razisea spicata non S. spicatus), S. strictus, S. ventricosus, S. villosus and S. wilburii are formalized. Seven new synonymies are presented for species of Chamaeranthemum, Dicliptera, Justicia and Stenostephanus, as well as lectotypifications in the first and latter two genera.

The New World 'justicioid' lineage (Acanthaceae: Acanthoideae: Justicieae) includes about 500 species and encompasses extensive variation in flower shape, size, and color along with remarkable diversity in anther, seed, and pollen mophology. Species richness of this lineage is due to the inclusion of the New World members of the polyphyletic genus Justicia in addition to five smaller Neotropical genera: Cephalacanthus, Clistax, Harpochilus, Megaskepasma, and Poikilacanthus. Although previous studies have shown that the New World 'justicioid' lineage is monophyletic, none have focused specifically on relationships among these plants nor has the current infrageneric classification of Justicia for the New World been tested. This is the first phylogenetic study to include a dense sample of taxa from the New World 'justicioid' lineage. We use DNA sequence data for five plastid, nuclear ribosomal ITS, and one low copy nuclear region (8315 bp) for 134 in-group taxa to estimate the phylogenetic framework for the group, and test the current infrageneric classification of New World Justicia. Most of the currently recognized sections of New World 'justicioids' are not monophyletic. On the other hand, our phylogenetic results identify nine major clades, many of which are supported by a combination of structural traits. The results of this study provide a foundation for the placement of other species of NewWorld Justicia that have yet to be sampled for phylogenetic analysis, as well as for future comparative studies of evolutionary processes and revisionary work on this diverse and complex lineage.

Abstract The New World ‘justicioid’ lineage (Acanthaceae: Acanthoideae: Justicieae) includes about 500 species and encompasses extensive variation in flower shape, size, and color along with remarkable diversity in anther, seed, and pollen mophology. Species richness of this lineage is due to the inclusion of the New World members of the polyphyletic genus Justicia in addition to five smaller Neotropical genera: Cephalacanthus, Clistax, Harpochilus, Megaskepasma, and Poikilacanthus. Although previous studies have shown that the New World ‘justicioid’ lineage is monophyletic, none have focused specifically on relationships among these plants nor has the current infrageneric classification of Justicia for the New World been tested. This is the first phylogenetic study to include a dense sample of taxa from the New World ‘justicioid’ lineage. We use DNA sequence data for five plastid, nuclear ribosomal ITS, and one low copy nuclear region (8315 bp) for 134 in-group taxa to estimate the phylogenetic framework for the group, and test the current infrageneric classification of New World Justicia. Most of the currently recognized sections of New World ‘justicioids’ are not monophyletic. On the other hand, our phylogenetic results identify nine major clades, many of which are supported by a combination of structural traits. The results of this study provide a foundation for the placement of other species of New World Justicia that have yet to be sampled for phylogenetic analysis, as well as for future comparative studies of evolutionary processes and revisionary work on this diverse and complex lineage.

This is the first study in Acanthaceae to provide a robust and well-sampled phylogenetic framework for the "justicioid" lineage (Acanthaceae: Acanthoideae: Justicieae), a clade that includes at least 1000 species that together occupy essentially the entire distributional range of the family as a whole. Species are morphologically diverse and occupy a wide variety of habitats. Although much progress has been made in understanding phylogenetic relationships within Acanthaceae, well-sampled phylogenetic studies are lacking for justicioids. DNA sequence data from six regions for 178 accessions from across the entire lineage were used to test monophyly and validity of 17 putative genera of justicioids on a global scale. Included among these genera is the species-rich genus Justicia for which we evaluate the current morphology-based classification with a focus on Old World taxa. Our results strongly support monophyly of New World justicioids, including all New World species of Justicia plus species assigned to at least five other smaller genera. Further, with a greatly expanded taxon sample, we confirm our earlier unexpected result that Diclipterinae are embedded within justicioids. As traditionally circumscribed, Diclipterinae lack the morphological traits that mark justicioids and thus had not previously been associated with that group. This study further extends this unexpected result by placing a number of Old World justicioids in a clade that is sister to Diclipterinae. Although some genera of justicioids, notably of Diclipterinae, are monophyletic, Justicia is grossly polyphyletic. We explore these results by examining the diagnostic utility of morphological characters for major clades with a focus on inflorescences, androecia, pollen and seeds. We further use our results as context for documenting evolutionary patterns of floral traits and pollinator relationships, as well as biogeographic patterns, across this species-rich and diverse clade.