Nicholas P. Tippery

Systematics of Vallisneria (Hydrocharitaceae)

Abstract Morphology, species delimitation, and interspecific relationships were evaluated in a phylogenetic context in the aquatic monocotyledon genus Vallisneria using a combination of morphological and molecular (nrITS, rbcL, trnK 5′ intron) data. Contrary to previous studies that recognized few species worldwide, we distinguished 12 species by molecular data, and an additional 2–3 species by morphological differences within groups that were invariant at the molecular level. Two new Vallisneria species ( V. australis , V. erecta ) are formally described. Other potentially novel species were detected from the cultivated material examined but require further study to elucidate their taxonomic status. Phylogenetic analyses indicated that vittate (caulescent) species (including Maidenia rubra) are not basal, but nested between two groups of rosulate (rosette) species. To preserve Vallisneria as monophyletic, a new combination is made ( V. rubra ) that accommodates the transfer of M. rubra to Vallisneria. Several taxonomic characters associated with the stigma morphology of pistillate flowers were found to represent suites of features related to pollination. In most cases, these character suites corresponded to a particular arrangement of filaments in the staminate flowers. The precise geographical origin of Vallisneria remains difficult to determine. However, we conclusively documented the presence of the Old World V. spiralis in Texas (United States), which constitutes the first authentic record of this nonindigenous species in North America.

Generic Circumscription in Menyanthaceae: A Phylogenetic Evaluation

Abstract Menyanthaceae consist of five genera of aquatic and wetland plants distributed worldwide. The three monotypic genera (Liparophyllum, Menyanthes, and Nephrophyllidium) are clearly differentiated morphologically, but the two larger genera (Nymphoides and Villarsia) contain several taxa of uncertain affinity. We undertook a phylogenetic analysis, using a combination of morphological and molecular data, to resolve relationships among species and to evaluate the current circumscription of genera. DNA sequence data for nuclear (ITS) and chloroplast (rbcL and trnK/matK) gene regions were largely congruent (by partition-homogeneity test), and a combined data phylogeny revealed several strongly supported relationships. Analyses using asterid outgroup taxa supported the monophyly of Menyanthaceae. Menyanthes trifoliata and Nephrophyllidium crista-galli comprised a clade sister to the remainder of the family. Species of Nymphoides, except N. exigua, resolved to a single, deeply-nested clade, indicating that the floating-leaved habit is derived evolutionarily within the family. The genus Villarsia comprised a paraphyletic grade toward Nymphoides, wherein the species resolved to three assemblages: (1) a shallowly nested clade containing V. albiflora, V. calthifolia, V. marchantii, V. parnassifolia, V. reniformis, and V. umbricola; (2) an isolated South African clade including V. manningiana and the type species, V. capensis; and (3) a heterogeneous clade of taxa from three genera, including V. exaltata, V. lasiosperma, and V. latifolia, plus the anomalous species V. capitata, V. congestiflora, Liparophyllum gunnii, and Nymphoides exigua. Our results indicate that the genera Menyanthes, Nephrophyllidium, and Nymphoides should be retained as circumscribed, with the exception that Nymphoides exigua should be restored to Villarsia. The genus Villarsia, however, eventually should be subdivided among monophyletic lineages, whereby in the strict sense Villarsia would contain only South African taxa.

Systematics and Phylogeny of Neotropical Riverweeds (Podostemaceae: Podostemoideae)

Abstract New World Podostemaceae (riverweeds) comprise approximately 135 species in 21 genera, most of which are of tropical distribution, shed pollen in monads, and belong to subfamily Podostemoideae. We undertook a phylogenetic study of Neotropical Podostemoideae using molecular (ITS, rbcL, trnL) and morphological data, to assess the monophyly of genera and their interrelationships. Extensive taxon sampling (38 taxa in 15 genera) revealed that the large genera Apinagia and Marathrum are not monophyletic as currently circumscribed, although several species of the former comprised a clade that could be delimited morphologically by the shared character of upright stems (i.e. anchored to the substrate only basally). Marathrum species were split geographically, with Central and South American taxa resolving in different clades. Oserya also comprised two geographically disparate clades, with the type species belonging to the South American clade. To establish the monophyly of Oserya, we erected a new genus Noveloa to accommodate the Central American species N. coulteriana and N. longifolia. The Central American Marathrum clade included the monotypic Vanroyenella, which we transferred to that genus as Marathrum plumosum. The genera Castelnavia and Rhyncholacis were monophyletic in our analyses; C. multipartita f. pendulosa was elevated to species rank as Castelnavia pendulosa. The monotypic Lonchostephus resolved within Mourera, with which it shares a number of morphological features that are found also in Tulasneantha (also monotypic), but which otherwise are unique in Podostemaceae. We recommend that Lonchostephus and Tulasneantha be merged with Mourera and provide the new combination Mourera monadelpha for the latter. Finally, an unexpected clade of morphologically diverse genera, including members of Apinagia, Jenmaniella, Lophogyne, Marathrum, and Monostylis, resolved with strong support but uncertain morphological integrity, as sister to all ingroup taxa except Mourera. However, nomenclatural changes in this group have not been made, pending additional taxon sampling and procurement of further molecular and morphological evidence.

Systematics of Two Imperiled Pondweeds (Potamogeton vaseyi, P. gemmiparus) and Taxonomic Ramifications for Subsection Pusilli (Potamogetonaceae)

Abstract Potamogeton is a taxonomically problematic genus of aquatic monocotyledons, which has received limited phylogenetic study using molecular data. The group is known for extensive vegetative plasticity, confusing patterns of morphological variation and propensity for hybridization. Potamogeton gemmiparus and P. vaseyi are of conservation concern in North America where both are listed as imperiled. These vegetatively similar species are particularly difficult to distinguish in the absence of floating leaves. We studied both species and putatively related taxa in subsection Pusilli (e.g. P. clystocarpus, P. foliosus, and P. pusillus) to elucidate relationships and to develop an identification method using molecular markers. Phylogenetic analyses of nrITS and trnK 5′ intron sequence data clearly endorse the recognition of P. gemmiparus and P. vaseyi as distinct species but call into question the subspecific circumscription of P. pusillus currently followed in North America. Our data resolved P. pusillus in a clade with P. foliosus, separated substantially from P. berchtoldii (= P. pusillus subsp. tenuissimus), thus supporting the recognition of P. berchtoldii as a distinct species. Using molecular cloning techniques, we documented three clear examples of interspecific hybridization (P. foliosus × P. pusillus, P. berchtoldii × P. vaseyi, and P. gemmiparus × P. vaseyi). Simple DNA polymorphisms also indicated several P. berchtoldii × P. gemmiparus hybrids. The narrowly distributed P. gemmiparus and P. clystocarpus are similar morphologically and genetically to the wide-ranging P. berchtoldii, with which they both hybridize. We recommend either the recognition of P. gemmiparus and P. clystocarpus as distinct species, or more suitably as subspecies of P. berchtoldii, for which two new combinations are provided: P. berchtoldii subsp. gemmiparus and P. berchtoldii subsp. clystocarpus.

Probing the Monophyly of the Sphaeropleales (Chlorophyceae) Using Data From Five Genes

Molecular phylogenetic analyses have had a major impact on the classification of the green algal class Chlorophyceae, corroborating some previous evolutionary hypotheses, but primarily promoting new interpretations of morphological evolution. One set of morphological traits that feature prominently in green algal systematics is the absolute orientation of the flagellar apparatus in motile cells, which correlates strongly with taxonomic classes and orders. The order Sphaeropleales includes diverse green algae sharing the directly opposite (DO) flagellar apparatus orientation of their biflagellate motile cells. However, algae across sphaeroplealean families differ in specific components of the DO flagellar apparatus, and molecular phylogenetic studies often have failed to provide strong support for the monophyly of the order. To test the monophyly of Sphaeropleales and of taxa with the DO flagellar apparatus, we conducted a molecular phylogenetic study of 16 accessions representing all known families and diverse affiliated lineages within the order, with data from four plastid genes (psaA, psaB, psbC, rbcL) and one nuclear ribosomal gene (18S). Although single‐gene analyses varied in topology and support values, analysis of combined data strongly supported a monophyletic Sphaeropleales. Our results also corroborated previous phylogenetic hypotheses that were based on chloroplast genome data from relatively few taxa. Specifically, our data resolved Volvocales, algae possessing predominantly biflagellate motile cells with clockwise (CW) flagellar orientation, as the monophyletic sister lineage to Sphaeropleales, and an alliance of Chaetopeltidales, Chaetophorales, and Oedogoniales, orders having multiflagellate motile cells with distinct flagellar orientations involving the DO and CW forms.

Phylogenetic Relationships and Morphological Evolution in Nymphoides (Menyanthaceae)

Abstract The cosmopolitan genus Nymphoides contains approximately 50 species that vary considerably in growth habit, inflorescence architecture, and in vegetative, floral, and seed morphology We undertook a phylogenetic study of 31 Nymphoides species, including all species native to Australia, to evaluate interspecific relationships and to infer the evolution of heterostyly and inflorescence architecture. Phylogenetic analysis of morphological data resolved several clades of species, but with poor branch support. Molecular data from nuclear (ITS) and plastid (matK/trnK) DNA sequences were significantly incongruent regarding the phylogenetic placement of many clades and species. Two major clades were resolved consistently: a clade sister to N. minima and the clade comprising these two lineages. Incongruent phylogenetic placements of several Nymphoides species were attributed to putative ancestral hybridization that produced conflicting phylogenetic signals between the maternally inherited cpDNA and the biparentally inherited nuclear DNA (subsequently homogenized to a single allelic variant by concerted evolution). Ancestral character state reconstruction indicated that the first Nymphoides species were heterostylous, followed by four independent transitions to homostyly and up to four subsequent reversions back to heterostyly. The evolutionary history of dioecy and gynodioecy could not be ascertained with confidence, owing to incomplete taxon sampling, poor resolution of crown clades, and incongruence between nuclear and plastid sequence data. Ancestral state reconstruction also indicated that the expanded inflorescence morphology found in several Australian and tropical Asian Nymphoides species represents the ancestral condition for the genus, from which a condensed morphology (found in most other Nymphoides species worldwide) evolved independently at least twice.

Hybridization in Hydrophiles: Natural Interspecific Hybrids in Najas (Hydrocharitaceae)

Abstract Pollination by water (hydrophily) is a highly specialized mechanism that occurs rarely among aquatic angiosperms, which mainly retain the reproductive systems reminiscent of their terrestrial ancestors. Hydrophily is abiotic and typically associated with unisexual flowers, factors that predictably would promote xenogamy and outcrossing. Yet, there have been few reports of hybridization involving waterpollinated plants (hydrophiles), with no firm evidence of natural interspecific hybridization. The genus Najas comprises about 40 species of submersed aquatic plants, all characterized by subsurface hydrophily. Hybridization in this genus has been suspected, but verified previously only among infraspecific taxa. In this study we document the first instance of interspecific hybridization in Najas using genetic evidence from three populations that were identifiable as N. guadalupensis but yielded polymorphic DNA sequence profiles. To facilitate our analysis we first conducted a phylogenetic survey of New World Najas taxa using nuclear and chloroplast markers. Alleles cloned from a biparentally-inherited locus (ITS) in these aberrant populations associated with two distinct but phylogenetically sister species (N. guadalupensis subsp. olivacea and N. flexilis) thus confirming their hybrid origin. In all cases the chloroplast markers associated with N. guadalupensis subsp. olivacea, implicating it as the maternal parent. The hybrid Najas plants occur at the edge of the sympatric range of the parental species. They possess no readily distinctive morphological features and require genetic analysis for confident detection. One population grows aggressively, raising concerns that at least some hybrid Najas plants represent a potential conservation threat. The possible hybrid ancestry of the endemic N. guadalupensis subsp. muenscheri also was assessed, but could not be confirmed or refuted by the data evaluated.

Transfer of Villarsia cambodiana to Nymphoides (Menyanthaceae)

Abstract Specimens of Villarsia cambodiana (Menyanthaceae), the only tropical Villarsia species, were collected from Vietnam, where the species had not been recorded. Molecular data were used to evaluate the phylogenetic position of V. cambodiana relative to 31 other Menyanthaceae taxa representing 11 species of Nymphoides and every species of Liparophyllum, Menyanthes, Nephrophyllidium, Ornduffia, and Villarsia. Phylogenetic analysis of nuclear (ITS) and chloroplast (matK/trnK, rbcL) DNA data strongly supported the resolution of V. cambodiana within Nymphoides, sister to N. aurantiaca. After plotting morphological data onto the molecular phylogenetic tree, we observed that leaf and inflorescence characters associated with an erect habit, which superficially would assign V. cambodiana to Villarsia, have arisen or been lost independently in several other Menyanthaceae species representing three genera. Moreover, several characteristics of this taxon, particularly seed morphology and an inflorescence with paired pedicels, are more consistent with those of Nymphoides than of Villarsia. We thus transfer V. cambodiana to Nymphoides under the new combination Nymphoides cambodiana.

Introduction of Glossostigma (Phrymaceae) to North America: a taxonomic and ecological overview

Field surveys in eastern North America confirm the naturalization of Glossostigma plants at 19 localities in four states: Connecticut, New Jersey, Pennsylvania, and Rhode Island. DNA sequence analysis of individuals from 14 sampled populations identifies these nonindigenous plants as Glossostigma cleistanthum, a species native to Australia and New Zealand. These results correct prior misidentifications of North American plants as G. diandrum. The earliest North American record of G. cleistanthum (1992) is from a Ramsar tidal wetland in Connecticut. Morphological analyses demonstrate that G. cleistanthum differs from G. diandrum by its longer leaves and ability to produce both cleistogamous and chasmogamous flowers in response to ecological conditions. Glossostigma cleistanthum has a high reproductive potential and spreads rapidly within and between both artificial and natural habitats. A survey of more than 100 lakes indicated that G. cleistanthum occurs most often in waters with high clarity and low pH, alkalinity, conductivity, and phosphorous. Because of its affinity for oligotrophic conditions, this species is a particular threat to pristine natural aquatic communities, which often contain imperiled plants.

Through thick and thin: Cryptic sympatric speciation in the submersed genus Najas (Hydrocharitaceae)

Cryptic sympatric species arise when reproductive isolation is established in sympatry, leading to genetically divergent lineages that are highly similar morphologically or virtually indistinguishable. Although cryptic sympatric species have been reported in various animals, fungi, and protists, there are few compelling examples for plants. This investigation presents a case for cryptic sympatric speciation in Najas flexilis, a widespread aquatic plant, which extends throughout northern North America and Eurasia. The taxon is noted for its variable seed morphology, which earlier research associated with cytotypes; i.e., diploids were characterized by thicker seeds and tetraploids by thinner seeds. However, cytotypes are not patterned geographically with diploid and tetraploid plants often found in close proximity within the same lake. Using digital image and DNA sequence analyses, we found that diploids and tetraploids are well-isolated and remain genetically distinct throughout their sympatric range, where sterile hybrids occur frequently. Incorporation of sequence data from the single-copy nuclear phytoene desaturase locus revealed further that the tetraploids are allopolyploid derivatives of N. flexilis and N. guadalupensis, the latter a closely related species with an overlapping distribution. We conclude that the taxon widely known as N. flexilis actually comprises two cryptic, sibling species, which diverged in sympatry by interspecific hybridization and subsequent chromosomal isolation. By comparing seed morphology of type specimens, we associated the names N. flexilis and N. canadensis to the diploids and tetraploids respectively. Additionally, the narrowly restricted taxon known formerly as N. muenscheri is shown via morphological and genetic evidence to be synonymous with N. canadensis.