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Nesom, G.L. 2010. See articles in Phytoneuron
Nesom, G.L. 2009. Taxonomy of Forestiera pubescens and Forestiera neomexicana (Oleaceae). Lundellia 12: 814.
Forestiera neomexicana is relatively constant in diagnostic features of vestiture and leaf shape across most of its range in the southwestern USA, from California to New Mexico and into western Texas. Apparent intermediacy in leaf shape and vestiture with F. pubescens, however, as well as glabrous forms of F. pubescens, have complicated identification. The two taxa are treated here as the eastern F. pubescens var. pubescens and the western F. pubescens var. parviflora, comb. nov. The ranges of the two taxa are mapped and variant forms are shown in Texas. Synonymy and typification are provided.
Nesom, G.L. 2009. Taxonomic overview of Ligustrum (Oleaceae) naturalized in the United States. Phytologia 91: 467482.
A key, morphological descriptions, and basic synonymy are provided for the eight species of Ligustrum known to be naturalized in North America north of Mexico: L. japonicum, L. lucidum, L. obtusifolium (including L. amurense), L. ovalifolium, L. quihuoi, L. sinense, L. tschonowskii, and L. vulgare. Identifications have been inconsistent particularly between L. sinense and L. vulgare and between L. japonicum and L. lucidum. The occurrence of L. quihuoi outside of cultivation in Arkansas, Mississippi, and Oklahoma is documented.
Nesom, G.L. 2009. Taxonomic notes on acaulescent Oxalis (Oxalidaceae) in the USA. Phytologia 91: 501526.
A key to species and typification summaries with descriptions, notes on variation, and geography are presented for 10 acaulescent Oxalis species occurring in the USA, both native and naturalized: O. articulata, O. caerulea, O. debilis, O. decaphylla, O. drummondii, O. intermedia, O. latifolia, O. metcalfei, O. triangularis, and O. violacea. Oxalis metcalfei (previously identified in the USA mostly as O. alpina) occurs in Arizona, Colorado, New Mexico, and Texas. Oxalis latifolia occurs in Arizona, New Mexico, and Texas, at the northern extremity of its range. Oxalis intermedia, native to the West Indies, has previously been known to be naturalized in the USA in Florida and is reported here from Louisiana and Texas. Oxalis debilis (including O. corymbosa) occurs across seven coastal states of the southeastern USA and is reported here for California by a voucher and for Washington by a sight record.
Nesom, G.L. 2009. Notes on Oxalis sect. Corniculatae (Oxalidaceae) in the southwestern United States. Phytologia 91: 527533.
Oxalis californica, O. pilosa, and O. albicans are distinct species of the southwestern USA and Mexico. Geographic summaries are provided and a species key includes these as well as O. corniculata, O. dillenii, and O. stricta, which also occur in the area. Oxalis californica is documented from south-central Arizona by collections from closely adjacent sites in Pinal and Maricopa counties in the Superstition Wilderness Area. Outside of its native range in California, and Arizona, and southwestern New Mexico, O. pilosa is reported from probable adventive occurrences in Nevada, Utah, and Oregon. Oxalis albicans is documented as an adventive in southern California.
Nesom, G.L. 2009. Again: taxonomy of yellow-flowered caulescent Oxalis (Oxalidaceae) in eastern North America. J. Bot. Res. Inst. Texas 3: 727738.
The taxonomy of Oxalis sect. Corniculatae is revised for eastern North America and contrasted with previous classifications and circumscriptions, particularly those of Eiten and Lourteig. Eight taxa, some previously recognized as subspecies or varieties, are recognized here at species rank. Oxalis stricta L. and O. dillenii Jacq. sensu stricto are appropriately identified in the sense that Eiten used the names. Oxalis florida Salisb. (= O. dillenii subsp. filipes) is a distinct species primarily of the Atlantic states and Gulf coast, less common in more inland regions. Oxalis priceae Small is a distinct species of the southeastern USA without infraspecific taxa; disjunct populations occur in northeastern Mexico. Oxalis texana (Small) Fedde (= Oxalis priceae subsp. texana) is treated as a distinct species of east Texas and adjacent Louisiana and Arkansas. Oxalis texana is close in morphology to O. dillenii sensu stricto and occurs sympatrically with it but distinct in geography and morphology from O. priceae sensu stricto. Oxalis illinoensis Schwegm. is geographically and morphologically distinct from O. grandis Small. Neotypes are designated for O. lyonii and O. illinoensis.
Nesom, G.L. and J.O. Sawyer. 2009. Frangula betulifolia and F. obovata (Rhamnaceae) are distinct species. Phytologia 91: 300307.
Frangula betulifolia var. obovata occurs in northern Arizona, Nevada, Utah, and Colorado and is geographically disjunct from var. betulifolia, which occurs in southern Arizona, New Mexico, Texas, and northern Mexico. The two taxa are consistently different in leaf shape and texture, and with their genetic isolation, each is appropriately treated at specific rank. A new combination is made: Frangula obovata (Kearney & Peebles) Nesom & Sawyer, comb. et stat. nov.
Nesom, G.L. 2009. Taxonomic overview of Eurybia sect. Herrickia (Asteraceae: Astereae). J. Bot. Res. Inst. Texas 3: 161167.
Herrickia horrida and five closely related species are included here within Eurybia sect. Horrida. These species are E. glauca, E. horrida, E. pulchra, and E. wasatchensis, as previously treated by Nesom, and two other species recently recognized by molecular evidence as close relatives: Eurybia kingii (D.C. Eat.) G.L. Nesom, comb. nov. (including Eurybia kingii var. barnebyana (Welsh & Goodrich) G.L. Nesom, comb. nov.) and Eurybia aberrans (A. Nels.) G.L. Nesom, comb. nov. The first five of these species were treated by Brouillet as a broadened genus Herrickia; the last was segregated as the monotypic genus Triniteurybia Brouillet, Urbatsch & Roberts. Molecular data indicate that Eurybia, Herrickia, and Triniteurybia constitute a 3-taxon grade at the base of the Machaerantherinae clade but morphological distinctions of Herrickia and Triniteurybia from Eurybia are trivial or non-existent and their separation from Eurybia at generic rank is based strictly on cladistic hypotheses. Nomenclatural summaries and geographic distributions are shown for the six species of Eurybia sect. Herrickia.
Nesom, G.L. 2009. Point of view: Authors initials in scientific names with multiple authorities. Phytologia 91: 6263.
Insistence on extended forms of author citations in all situations seems unnecessary, especially where brevity and easy comprehension are concerns. Additions of initials in citations of multiple authors load up text with unnecessary and ponderous details.
Nesom, G.L. 2008. Ranunculus ficaria (Ranunculaceae), naturalized in Texas. J. Bot. Res. Inst. Texas 2: 741742.
Ranunculus ficaria is documented to grow outside of cultivation in Tarrant County, where it is found along creek banks in Fort Worths Overton Park. Seeds are sterile and the plants reproduce asexually by bulbils produced by the roots and in leaf axils.
Nesom, G.L. 2008. Classification of subtribe Conyzinae (Asteraceae: Astereae). Lundellia 11: 838.
Subtribe Conyzinae includes Erigeron, New World Conyza, the North American genus Aphanostephus, and a small group of South American species segregated as the genera Apopyros, Darwiniothamnus, Hysterionica, Leptostelma, and Neja. Erigeron is the only genus with species native to regions outside of the New World. About 500 species are included in the subtribe. All North American, Central American, and South American species of Erigeron are included in the present treatment and assigned to one of the 35 sections recognized here. Ten new sections of Erigeron are recognized: sect. Disparipili Nesom, sect. nov., sect. Filifolii (Rydb.) Nesom, comb. et stat. nov., sect. Gyrifolium Nesom, sect. nov., sect. Lonchophylli Nesom, sect. nov., sect. Meridionales Nesom & N. Andrus, sect. nov., sect Microcephalum Nesom, sect. nov., sect. Quercifolium Nesom, sect. nov., sect. Radicati (Rydb.) Nesom, comb. et stat. nov., sect. Rhizonexus Nesom, sect. nov., and sect. Terranea (Colla) Nesom, comb. et stat. nov. Conyza is at least biphyletic; each of the groups is represented in the treatment but not all of the South American species are included. Molecular data have made it clear that traditional, North American species of Erigeron form the basal and terminal clades in the evolutionary topology of the subtribe, thus Conyza, Aphanostephus, and the other segregate genera have arisen from within the branches of Erigeron. Erigeron, as currently treated and tentatively maintained here, is paraphyletic. Broad taxonomic alternatives that include only monophyletic taxa are (1) to treat the whole subtribe as Erigeron or (2) to recognize Aphanostephus or Aphanostephus, Conyza, and the other South American segregates and at least an additional 5 to 10 new generic-level segregates from species groups traditionally treated as North American Erigeron.
Nesom, G.L. 2008. Taxonomic review of Solidago petiolaris and S. wrightii (Asteraceae: Astereae). Phytologia 90: 2135.
Solidago petiolaris is treated to include three morpho-geographic entities. Plants east of the Mississippi River are var. petiolaris; those west of the Mississippi are var. angusta and var. wardii. Phyllaries of var. angusta (in the eastern part of the western range) are glandular; phyllaries of var. wardii (in the western part are eglandular and finely strigose. Solidago wrightii is closely similar to S. petiolaris, especially where their ranges approach each other, and they show parallel trends of variation in leaf shape and involucral vestiture. Within S. wrightii, glandular plants apparently are populational variants without geographic coherence and are treated here as S. wrightii forma adenophora (Blake) Nesom, comb. et stat. nov. A narrow-leaved race near the southeastern corner of the range of the species (in Chaves Co. and Eddy Co., N.M., and Culberson Co., Tex.) is recognized as S. wrightii var. guadalupensis Nesom, var. nov.
Lipscomb, B.L. and G.L. Nesom. 2007. Galium parisiense (Rubiaceae) new for Texas, and notes on its taxonomy. J. Bot. Res. Inst. Texas 1: 12371300.
Galium parisiense var. leiocarpum is documented as a first record for Texas and South Carolina. Other localities in the eastern U.S.A. are mapped for the glabrous-fruited expression of G. parisiense (var. leiocarpum), bristly-fruited G. parisiense (var. parisiense), and the closely related, glabrous-fruited G. divaricatum. All taxa are European natives. In both North America and Europe, var. parisiense and var. leiocarpum have distinct geographic ranges and occur sympatrically in some areas. Galium divaricatum occurs sympatrically at least with var. leiocarpum. We suggest that specific rank is appropriate for each of the three taxa, as G. parisiense L., G. divaricatum Pourret ex Lam., and G. anglicum Hudson (= G. parisiense var. leiocarpum).
Nesom, G.L. 2007. Distribution of Gamochaeta (Asteraceae: Gnaphalieae) in Texas, Oklahoma, Arkansas, and Louisiana. J. Bot. Res. Inst. Texas 1: 11251130.
Distributions of seven species of Gamochaeta are mapped at county level in Texas, Oklahoma, Arkansas, and Louisiana: G. antillana, G. argyrinea, G. calviceps, G. chionesthes, G. coarctata, G. pensylvanica, and G. purpurea. Gamochaeta purpurea is the only species known from pre-1900 collections. Gamochaeta coarctata and G. chionesthes are known only from collections made after 1967; the latter apparently is spreading rapidly but has not reached Texas and Oklahoma.
Nesom, G.L. 2007. Notes on the disarticulation of Xylothamia (Asteraceae: Astereae). J. Bot. Res. Inst. Texas 1: 145148.
The primarily Mexican genus Xylothamia was originally described with nine species, but molecular evidence subsequently indicated that these species are divided into two separate evolutionary lineages. One of these groups (four species) was transferred to the Caribbean genus Gundlachia, while the other (five species) was split into four separate new genera. An alternative and reasonable taxonomic solution proposed here is to maintain the group close to Gundlachia as the genus Xylothamia and treat the remaining five species within a single genus.
Nesom, G.L. and B.L. Turner. 2007. Taxonomic review of the Xanthisma spinulosum complex (Asteraceae: Astereae). Phytologia 89: 371389.
Xanthisma incisifolium, X. glaberrimum, X. paradoxum (Turner & Hartman) Turner & Nesom, comb. et stat. nov., and X. scabrellum (Greene) Turner & Nesom, comb. nov., do not intergrade with other taxa of the complex and are treated at specific rank. In regions of sympatry, X. spinulosum var. spinulosum, var. gooddingii, var. chihuahuanum, and var. austrotexanum intergrade and are maintained at varietal rank. Xanthisma spinulosum var. hartmanii Turner & Nesom, var. nov., is described from northern Coahuila. County-level dot maps document distribution of the taxa.
Nesom, G.L. 2006. Taxonomic overview of the Heterotheca villosa complex (Asteraceae: Astereae). Sida 22: 376380.
Heterotheca villosa (as treated by Semple 1996, 2006) is a complex species with nine varieties, most of which are sympatric in various degrees. Heterotheca villosa var. nana and H. villosa var. scabra are essentially allopatric and intergrade little, but each is widely sympatric with H. villosa and distinct from it. Recognition at specific rank accurately reflects the status of var. nana and var. scabra, and they are treated here, respectively, as Heterotheca horrida (Rydb.) Harms and Heterotheca polothrix Nesom, nom. et stat. nov. Heterotheca stenophylla sensu stricto is distinct from H. stenophylla var. angustifolia (sensu Semple) and sympatric with it, and the latter is appropriately treated as H. villosa var. angustifolia (Rydb.) Harms. The New Mexico endemic Heterotheca villosa var. sierrablancensis Semple is raised to specific rank as Heterotheca sierrablancensis (Semple) Nesom, comb. et stat. nov. Identifications of vars. villosa, foliosa, ballardii, and minor (all sensu Semple) require arbitrary judgements because of their broad sympatry and extensive intergradation. The distinction between var. pedunculata and H. zionensis is not clear, and both taxa apparently intergrade broadly with more typical H. villosa. Variety depressa is maintained at specific rank as H. depressa (Rydb.) Dorn. Maps show the generalized distributions of the taxa of the H. villosa complex sensu Semple, and a nomenclatural summary outlines an alternative taxonomy.
Nesom, G.L. 2006. Taxonomic review of Symphyotrichum patens (Asteraceae: Astereae). Sida 22: 10751080.
The eastern North American Symphyotrichum patens has been treated by Jones (1983, 1992) and other botanists to include var. patens, var. patentissimum, and var. gracile. These taxa have been distinguished primarily by habit, involucral size and vestiture, and phyllary orientation. Morphological distinctions between var. patens and var. gracile have been viewed as overlapping and the two taxa have been interpreted as sympatric over a wide region; the present study concludes that it is not possible to distinguish them in an unarbitrary or evolutionarily meaningful way, and var. gracile is not recognized. Variety patens sensu lato apparently comprises two diploid and three or four tetraploid population systems. Variety patentissimum is morphologically distinct and consistently tetraploid, and it intergrades with tetraploid var. patens where their ranges are contiguous or overlapping. A county-level map shows the distribution of the two infraspecific taxa of S. patens, as interpreted in the present study. A similar map shows ploidal distribution within the species, based on data available from previous studies.
Nesom, G.L. 2005. Infrageneric classification of Liatris (Asteraceae: Eupatorieae). Sida 21: 13051321.
A formal classification divides the species of Liatris (blazing star or gayfeather) into 5 'sections,' two of which are further divided into 'series.' The classification is based on morphological similarities among the 37 species and hypotheses regarding their evolutionary relationships.
Nesom, G.L. 2005. Broadened concept of Liatris helleri (Asteraceae: Eupatorieae). Sida 21: 13231333.
A much-broadened concept is documented for a species formerly considered to be rare and narrowly endemic to a small area in the North Carolina mountains. In the amended concept, it occurs more broadly through North Carolina and also in Virginia and West Virginia (and is no longer rare).
Nesom, G.L. 2004. New species of Gamochaeta (Asteraceae: Gnaphalieae) from the eastern United States and comments on similar species. Sida 21: 717742.
Two new species of Gamochaeta (cudweed) are described from the eastern USA. One occurs abundantly in at least 19 states, and the other is known from 9 states. Both tend to be weeds of roadsides and other 'weedy' sites, and it is possible that both species may be native to South America, where they also have been previously undetected.
Nesom, G.L. 2004. New distribution records for Gamochaeta (Asteraceae: Gnaphalieae) in the United States. Sida 21: 11751186.
Various state records are reported for species of Gamochaeta (cudweed). Two of the species are first reported for the USA. For the 12 species of the genus known from the USA, a hypothesis of nativity is given, with acknowledgement that because the species tend to be extremely weedy, it is difficult to be certain of their native area.
Nesom, G.L. 2004. Notes on typification in Pluchea (Asteraceae: Plucheeae). Sida 21: 5964.
In order to clearly establish the identity of various names used for species of North American Pluchea (camphorweed), a particular herbarium specimen is associated with each of the names. This is not something that was consistently done for old names (most pre-1900), but it is required for new ones.
Nesom, G.L. 2004. Erigeron peregrinus and Erigeron glacialis (Asteraceae: Astereae). Sida 21: 665672.
A daisy fleabane widespread and common in high elevation habitats of western North America is treated as a full species (E. glacialis). Since 1943 it has been regarded as a subspecies of E. peregrinus, but even where the two species come into close contact, reproductive isolation holds them as two distinct and recognizable entities.
Nesom, G.L. 2004. Pseudognaphalium canescens (Asteraceae: Gnaphalieae) and putative relatives in western North America. Sida 21: 781790.
Five species of cudweeds mostly centered in California have been recently treated (in the Jepson Manual) as subspecies of a single species. Evidence is presented for regarding each of them as a separate species. Pseudognaphalium thermale is brought into the genus with a new combination, and distribution maps and a key are included.
Nesom, G.L. 2004. Generic placement of Chaptalia hintonii (Asteraceae: Mutisieae). Sida 21: 929934.
In a 1998 publication, Argentinian botanist Katinas placed the Mexican species Chaptalia hintonii in the otherwise Old World genus Gerbera. The author takes issue with her judgement and gives evidence supporting the continued treatment of C. hintonii within Chaptalia, where its closest relatives are classified.
Nesom, G.L. 2004. Asteraceae from wool mill sites in South Carolina, including new records for North America. Sida 21: 12151224.
Documentation is given for 73 taxa of Asteraceae collected in 19571960 from wool mill sites in Berkeley County and Florence County, South Carolina. Twenty-eight (28) of these taxa are first reports for the flora of South Carolina; seventeen (17) others represent the first documentation for earlier reports for the state. Six (6) are first reports for North America: Chevreulia sarmentosa, Gamochaeta argentina, and Panphalea heterophylla (native to South America), and Peripleura arida, Stuartina hamata, and Vittadinia sulcata (native to Australia). Calotis cuneifolia (native to Australia) is reported for North America for the second time. Fifty-nine (59) of the 73 taxa are not native to South Carolina; of these, 29 are native to continents other than North America, while 30 are native to North America but from regions outside of the state.
Nesom, G.L. 2001. Taxonomic review of Chrysogonum (Asteraceae: Heliantheae). Sida 19: 811821.
Chrysogonum is a genus of the eastern USA well-known in cultivation for its low growth and small, golden-yellow sunflowers. The author evaluates previous taxonomy and finds that the species has three varieties (not just two), each of which has a separate geography and morphological appearance.
Nesom, G.L. and J.T. Kartesz. 2000. Observations on the Ludwigia uruguayensis complex (Onagraceae) in the United States. Castanea 65: 123125.
Ludwigia uruguayensis is known to comprise a decaploid entity (L. hexapetala) and a hexaploid one (L. grandiflora, including the type of L. uruguayensis), but the two chromosomal races differ only by quantitative, intergrading morphological features, a large portion of their genome is hypothesized to be shared, and they are known to produce hybrids of intermediate morphology in regions of sympatry. Ludwigia hexapetala is the more common, but both occur in the southeastern United States. We agree in general with earlier studies regarding the nature of the distinction between the two entities but suggest that a more reasonable treatment of them would be as subspecies within a single species: L. grandiflora subsp. grandiflora and L. grandiflora subsp. hexapetala, comb. et stat. nov.
Nesom, G.L. 1994. Taxonomic overview of Aster sensu lato (Asteraceae: Astereae), emphasizing the New World species. Phytologia 77: 141297.
Nesom, G.L. 1992. A new species of Castilleja (Scrophulariaceae) from south-central Texas with comments on other Texas taxa. Phytologia 72: 209230.
Castilleja genevievana sp. nov. is described from Crockett, Pecos, Upton, and Val Verde cos., Texas, and one closely adjacent locality in Coahuila, Mexico. It is most closely related to C. integra and C. purpurea var. citrina but is allopatric with both and morphologically distinctive in its entire leaves, unbranched trichomes, and yellow floral bracts and calyces. Castilleja wootonii (the type from southeastern New Mexico) is the correct name for the species in Jeff Davis Co., Texas, previously known as C. ciliata and assumed to be a narrow endemic. Castilleja elongata, which has been recognized primarily from Brewster Co., Texas, and a proposed but yet unpublished species endemic to Jeff Davis Co. are interpreted as merely intergrading elements of the widespread and variable C. integra. Castilleja latebracteata (the type from Texas) is a synonym of Castilleja rigida (the type from Chihuahua), a species primarily distributed in northern Mexico. Castilleja tortifolia (the type from Texas) is conspecific with the earlier named C. mexicana, also most abundant in northern Mexico.