must adhere to the nomenclatural Taxonomy and Nomenclature of Baldcypress, rules set by the International Code Pondcypress, and Montezuma Cypress: One, of Botanic Nomenclature (Greuter et al., 2000), including those dealing Two, or Three Species? with status, typification, and priority of names. 1,3 2 There are several very useful Geoffrey C. Denny and Michael A. Arnold online nomenclatural data bases that are readily accessible. These include ADDITIONAL INDEX WORDS. scientific name, binomial, variety, subtaxa, Taxodium the International Plant Names Index distichum var. distichum, var. imbricarium, var. mexicanum, Taxodium ascendens (2006), the Missouri Botanical var. nutans, Taxodium mucronatum Garden’s VAST nomenclatural data- base accessed through the W3TRO- SUMMARY. As interest in issues such as seed source, provenance, genetic pollution, PICOS interface (Missouri Botanical and threatened and endangered plant species grows, so does the need for an understanding of the relatedness and evolutionary history of plants. Appropriate Garden, 2006), and the U.S. Depart- taxonomy and nomenclature become much more important. Taxodium (L.) Rich. ment of Agriculture (USDA) is a genus of landscape trees included in many plant materials courses across the National Plant Germplasm System country. It has been treated variously in the horticulture literature as having one, (USDA, 2006). two, or three species. The most appropriate treatment is one species with three botanical varieties: baldcypress [Taxodium distichum (L.) Rich. var. distichum], pondcypress [T. distichum var. imbricarium (Nutt.) Croom], and montezuma Taxonomy of Taxodium cypress [T. distichum var. mexicanum Gordon]. Baldcypress, pondcypress, and montezuma cypress are three taxa he appropriate taxonomy and incorrect taxonomic classification is recognized historically in the genus nomenclature for plant taxa used. Taxodium. Baldcypress has a range (taxonomic groupings) are Often horticulturists are frus- along the Atlantic and Gulf Coast T Plains of the United States. It can often overlooked by the nursery trated, irritated, and sometimes industry and may seem of little impor- baffled by the seemingly arbitrary be found naturally as far north as tance. However, names frequently do nomenclatural changes taxonomists Maryland and Illinois, and south into not reflect the most current taxo- and systematists make to plants. We Florida and central Texas (Middleton nomic classification. This may seem often wonder aloud, ‘‘Why can’t they and McKee, 2004). Pondcypress is of little importance. However, names just leave things alone?’’ We often ask restricted in distribution to Florida take on a new importance when we students the importance of scientific and the Gulf Coast east of Texas, realize that binomials are intended to names while teaching plant materials and up the Atlantic coast to North Carolina (Middleton and McKee, convey information beyond distin- classes. Answers range from ‘‘because 2004). Montezuma cypress is the guishing one plant from another. plants can have more than one com- southernmost taxa, occurring in Binomials reflect relationships and mon name’’ to ‘‘so each plant has a Mexico and far southern Texas relatedness among groups of plants. standard name that everyone uses.’’ (Turner and Watson, 1999). We ignore that information if we do Almost invariably the answers deal T. distichum is widely accepted as not use the most appropriate name as with distinguishing plants from each decided by a taxonomic specialist. the correct name for baldcypress other. We spend very little time on (Arnold, 2002; Liberty Hyde Bailey Ecologically and environmentally the importance of scientific names for friendly industry practices are grow- Hortorium, 1976; Lickey and conveying relatedness among plants Walker, 2002; Lickey et al., 2002; ing in importance along with public or evolutionary history of taxa. Yet, interest. Issues such as provenance are McMillian, 1974; Murphy and this is the objective of the hierarchical Stanley, 1975; Schopmeyer, 1974; receiving more and more interest and system Linnaeus created. Otherwise, research (Bresnan et al., 1996; Gir- Tsumura et al., 1999; Turner and all that would matter is that each taxon Watson, 1999; Vines, 1960; Watson, idhar et al., 1995; Lickey et al., 2002; has a unique name. Name changes are McMillian, 1974; Schrader and 1983, 1993). Disagreement arises not always meaningful if all we are Graves, 2000; Shoemake et al., with respect to the classification of concerned with is distinguishing one 2004; Wood et al., 1998). Appropri- the other two taxa. Authors treat the plant from another. However, as ate classification of taxa is of the genus as having three species (Arnold, interest grows for issues like seed utmost importance in these types of 2002; Griffiths, 1994; Kru¨ssmann, source, provenance, genetic pollu- studies, because they attempt to 1985; Turner and Watson, 1999); investigate the geographic compo- tion, and threatened and endangered others, as two species, with one hav- nent to genotypic variation. Errone- plant species, so does the need for an ing two botanical varieties (Liberty ous conclusions may be drawn if understanding of the relatedness and Hyde Bailey Hortorium, 1976; Vines, evolutionary history of plants. Cor- 1960). Pondcypress has been treated Department of Horticultural Sciences, Texas A&M rect plant nomenclature becomes as a distinct species, T. ascendens University, College Station, TX, 77843-2133. more important regarding to which Brongn., by some authors (Arnold, 1PhD student. genus a species belongs or whether 2002; Griffiths, 1994; Kru¨ssmann, 2Professor of Landscape Horticulture. two taxa are distinct species or sub- 1985; Turner and Watson, 1999) and 3Corresponding author. E-mail: [email protected] species or botanical varieties. Names as a botanical variety of T. distichum by
• January–March 2007 17(1) 125 TEACHING METHODS others (Liberty Hyde Bailey Hortorium, Table 1. Key to botanical varieties of Taxodium distichum. 1976; Lickey and Walker, 2002; 1a. Determinate short shoots mostly ascending in a vertical plane; awllike leaves narrowly Lickey et al., 2002; Murphy and lanceolate, 0.1–0.4 inch long, appressed, and imbricate in five to eight ranks on Stanley, 1975; Schopmeyer, 1974; shoots...... var. imbricarium St. Hilaire, 2001; Vines, 1960; Watson, 1b. Determinate short shoots mostly spreading in a horizontal plane; flattened leaves 1983, 1993). The botanical variety narrowly linear, 0.2–0.6 inch long, divergent, and appearing two ranked on name most commonly assigned is shoots...... 2 T. distichum var. nutans (Ait.) Sweet. 2a. Leaves deciduous; branches (catkins) containing male cones short and crowded, Pondcypress has been segregated from often divided into compact secondary branches...... var. distichum baldcypress based on vegetative mor- 2b. Leaves semievergreen; branches (catkins) containing male cones long and slender, phology, sometimes in combination open, made up of single cones or clusters of several cones ...... var. mexicanum with poorly defined and inconsistent z1 inch = 25.4 mm. habitat or community-type differ- Adapted from Watson (1983) and Correll and Johnston (1970). ences (Watson, 1983). Watson (1983) reported that there exist numerous individuals and populations that nological characters,’’ as indicated by Nomenclature ‘‘exhibit morphological intermediacy Watson (1993) in his treatment of After the taxonomic questions or curious admixtures of the characters Taxodium for the Flora of North are answered, the question of appro- representative of the morphological America. McMillian (1974) indi- priate nomenclature arises. Baldcy- extremes. (p. 192)’’ This phenomenon cated morphological and physiolog- press was originally described by has also been personally observed by ical gradients exist between T. Linnaeus (1753) as Cupressus disti- the authors of this paper. Watson distichum and the Mexican popula- cha. Richard (1810) transferred to the (1983) contends that the vegetative tions. Montezuma cypress has been genus Taxodium as T. distichum. The and ecological differences are insuffi- planted in close proximity in areas of correct botanical name for baldcy- cient to support specific rank for pond- central Texas to native baldcypress press is T. distichum var. distichum cypress. Also, there is no significant stands. Large numbers of offspring when the genus is treated as one difference in reproductive morphology with intermediate characteristics and species with three botanical varieties. and anatomy, embryology, leaf flavo- heavy seed set were observed there in Pondcypress is commonly cited as noid and bioflavonoid profiles, and the fall 2003 (G. C. Denny, pers. T. distichum var. nutans (Ait.) Sweet, nuclear DNA content of meristematic obs.). These observations, in the when it is given botanical variety status root cells (Watson, 1983). All these absence of molecular evidence, indi- (Liberty Hyde Bailey Hortorium, characters have been reliable criteria cate that botanical variety status is 1976; Murphy and Stanley, 1975; for distinguishing between species more appropriate for montezuma Schopmeyer, 1974; St. Hilaire, 2001; of other conifers (Watson, 1983). cypress. See Table 1 for a key to the Vines, 1960). According to Watson Therefore, Watson (1983) classified botanical varieties of T. distichum. (1983), Cupressus disticha (L.) var. pondcypress as a botanical variety of T. distichum. Also, Tsumura et al. (1999) concluded that pondcypress should Table 2. Abbreviated synonymy for baldcypress, pondcypress, and montezuma only be given botanical variety status cypress. based on DNA analysis using cleaved amplified polymorphic sequences. Baldcypress Based on allozyme analysis, botanical 1810. Taxodium distichum (L.) Richard var. distichum variety status for pondcypress was 1810. Taxodium distichum (L.) Richard also supported by Lickey and Walker 1753. Cupressus disticha L. (2002). 1789. Cupressus disticha var. nutans Aiton Montezuma cypress is often 1827. Taxodium distichum var. nutans (Aiton) Sweet treated as a distinct species, T. 1938. Taxodium distichum f. confusum Palmer and Steyermark mucronatum Tenore (Arnold, 1939. Taxodium distichum f. pendens Rehder 2002; Liberty Hyde Bailey Horto- Pondcypress rium, 1976; Creech and Yunlong, 1837. Taxodium distichum var. imbricarium (Nuttall) H.B. Croom 2003; Griffiths, 1994; Kru¨ssmann, 1818. Cupressus disticha L. var. imbricaria Nuttall 1985; McMillian, 1974; St. Hilaire, 1833. Taxodium ascendens Brongniart 2001; Turner and Watson, 1999; 1902. Taxodium imbricarium (Nuttall) R.M. Harper Vines, 1960). However, according 1927. Taxodium ascendens var. nutans (Aiton) Rehder, pro synonym, non Aiton to Watson (1983) it has also been Taxodium ascendens var. nutans (Aiton) Sweet, sensu authors, non Aiton treated as a botanical variety, T. dis- 1982. Taxodium ascendens ssp. nutans (Aiton) E. Murray, pro synonym, non Aiton tichum var. mexicanum Gordon. Montezuma cypress DNA and phytochemical analyses 1858. Taxodium distichum var. mexicanum (Carrie`re) Gordon are not available for montezuma 1855. Taxodium mexicanum Carrie`re cypress. However, there are several 1853. Taxodium mucronatum Tenore factors that suggest botanical variety 1854. Taxodium montezumae Decaisne status is appropriate. Montezuma 1906. Taxodium distichum var. mucronatum (Tenore) A. Henry cypress differs only by ‘‘minor phe- Adapted from Watson (1983) and Missouri Botanical Garden (2006).
126 • January–March 2007 17(1) nutans was originally described by Giridhar, J., B. Pai, and W.R. Graves. mobot.mobot.org/W3T/Search/vast. Aiton (1789) and C. disticha var. imbri- 1995. Seed source affects seedling devel- html>. caria by Nuttall (1818). It appears opment and nitrogen fixation of Maackia amurensis. J. Environ. Hort. 13:142–146. Murphy, J.B. and R.G. Stanley. 1975. nutans has priority. However, the plant Increased germination rates of baldcy- described by Aiton (1789) was not Greuter, W., J. McNeill, F.R. Barrie, press and pondcypress seed following pondcypress; rather, it was a long-leaf, H.M. Burdet, V. Demoulin, T.S. Filguei- treatments affecting the seed coat. drooping form of baldcypress (Watson, ras, D.H. Nicolson, P.C. Silva, J.E. Skog, Physiol. Plant. 35:135–139. P. Trehane, N.J. Turland, and D.L. 1983). Therefore, imbricaria has prior- Nuttall, T. 1818. The genera of North ity (Watson, 1983). The name imbri- Hawksworth (eds.). 2000. International code of botanical nomenclature (St. Louis American plants. Vol. 2:224 (1971. Fac- caria became imbricarium in 1837 simile of 1818 ed.). Hafner Publishing, when Croom (1837) classified pondcy- Code). Regnum Vegetabile 138. Koeltz Scientific Books, Ko¨nigstein, Germany. New York. pressasabotanicalvarietyofT. dis- tichum (Watson, 1983). The correct Griffiths, M. 1994. The new Royal Horti- Richard, L.C.M. 1810. Note sur les plantes dites conifers. Annales du muse´- botanical name for pondcypress is T. cultural Society dictionary: Index of garden plants. Timber Press, Portland, um national d’histoire naturelle 16:296– distichum var. imbricarium (Nutt.) 299. Croom adopted by modern authors Ore. (Lickey and Walker, 2002; Lickey International Plant Names Index. 2006. Schopmeyer, C.S. 1974. Seeds of woody et al., 2002; Tsumura et al., 1999; The International Plant Names Index. plants in the United States. USDA Hand- Watson, 1983, 1993). 12 June 2006. • January–March 2007 17(1) 127