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TURNER CROTON BIGBENDENSIS (EUPHORBIACEAE) REVISITED James Henrickson INTRODUCTION dioecious wide ranging, distinctive, Croton (Euphorbiaceae) a dioicus Cav. neomexicanus Mull.Arg.] is [C. by The characterized species Perennial of Croton Drepadenium Mull.Arg. (Webster 1993). is section (Raf.) and leaves moderately short petioles, dichotomous styles, valvate, eglandular sepals, petals absent, mm The species with 0.3-0.5 in diameter. a distinctive silvery canescence formed by fringed peltate scales occurs from west-central and trans-Pecos Texas and adjacent New Mexico, southward into arid regions of San Durango, Zacatecas, Mexico in the states of Chihuahua, Coahuila, Nuevo Le6n, Tamaulipas, Veracruz, iuis Potosi, and Oaxaca. Hidalgo, Tlaxcala, Mexico, Puebla, “bigbendensis,” char- Turner with the epithet (2004) distinguished from a separate species, C. dioicus, aaerized internodes and linear-lanceolate leaves as being a bushier with longer upper-stem larger, plant, Grande Hudspeth, 5-7 Rio in along the times as long as wide. He noted that the species is restricted to areas becoming Mexico) Kcsidioand from adjacent Coahuila, Brewster one specimen cited counties Texas (with of and where they fominant occur with dioicus in sandy habitats. He further noted that the species does not C. , ** new be good cryptic a near contact” they do not appear intergrade. He considered his species to to no or were quantitative; proposed species "biological” the used delineate species. All the characteristics to dilative characteristics were noted or implied. 22- (Turner one holotypes, pistillate Unfortunately, in his paper he two herbarium specimens as cites same time Though the f^A) and one number. collected at staminate Turner 22-204B each given a separate ( ), Nomenclature (McNeill the same Code of Botanical population the International (a single gathering), 4 " separate 2006 numbers be designated as to > does not allow two specimens with two separate separate one specimen or ?»ypes taxon the [ICBN name or infraspecihc is Art. 9.1-”A holotype of a or a species and (emphasis mine)] Ration nomenclature type used by the author, or designated by the author as the comm.; (Kanchi Gandhi, pers. an and considered alidly published is specimen one sheet of a single Name A holotype Index). t KSNAn. but gathering (Art 8.2), than one plant in a single 8-3) if clearly noted,; 296 the designation of two separately numbered specimens, mounted on separate sheets, each named asholotypt & (Turner 2004, pp. 81 82), renders the specimens syntypes (Art. 9.4, ex. 1) and therefore no holotype exists name and the not validly published. is my new Chihuahuan As his proposed taxon occurs within the Desert, area of interest, analyzed I characteristics used by Turner (2004) to distinguish the two taxa using specimens he annotated in the maximum TEX-LL herbarium. initially measured total stem length and internode length as an indication I of plant size, leaf blade length and width as well as petiole length from one larger leaf on each specimen. 1 when on also recorded soil type (clay, gypsum, or sandy-well drained) for each collection noted the label Petiole length and total stem length, while quite variable, were not further used because the petiole length generally correlated with leaf size and the total stem length displayed in specimens too often reflects the portion collected, not total plant size. Data on soil type were very spotty from specimens outside west Texas so this was not used in the analyses but discussed below. While criticism can be raised from taking is make measurements from herbarium specimens, these are the specimens used to taxonomic decisions and, while imperfect, they represent samples of a species and they are readily available. METHODS Data were collected from specimens TEX-LL (n=296) with 41 from trans-Pecos Texas identified by all at my 72 from Turner as “Croton bigbendensis” plus six of specimens that are clearly referable to that taxon, typical Croton dioicus in trans-Pecos Texas (west of the River), 98 from C. dioicus from cis-Pecos Texas (east of New the Pecos River) and adjacent Mexico, and 85 from from Mexico. For the quantitative analysis C. dioicus mm) and measurements of longest internode present on each specimen, as well as the longest leaf length (in mm) its width (in and these were used to formulate a leaf length/width ratio. RESULTS mm maximum length/leaf Measurements of intemode length in (abscissa) graphed against a ratio of leaf bigbendensis width indicating shape shown putative “Croton leaf (ordinate) are in Figure Collections of 1. from with those are distinguished by open by shapes circles; those of Croton dioicus are indicated solid Mexico from trans-Pecos Texas indicated by solid circles, from cis-Pecos Texas by solid squares, and those by solid triangles. specimens- The means and "bigbendensis standard deviations of four recorded from the characteristics present from the specimens from each of the three areas of C. dioicus and from all combined C. dioicus are deviations in Table 1. While the means of leaf and intemode lengths are distinctive, the large standard wide indicate the variation found in Croton “bigbendensis.” . longmtemw® The graph shows many by (Fig. 1) that while specimens of “bigbendensis” are characterized — cUSl and/or narrow two distinct leaves, the measurements blend into those of C. dioicus there are not , “bigben of data points indicating well defined character and fourth (10 of 41) of the differentation, a ^ “bigbendensis data points are nested within those of C. dioicus. The specimens of the proposed taxon ^ 50. 1/w maximum averaging leaf ratios averaging ranging from and intemode lengths 5.9, 3-14.4, averaging^ mm. ranging from 31-98 Specimens have 1/w ratios assignable to C. dioicus, in contrast, leaf mm. 11-72 ranging from and maximum mm, from 1.4-6.8, ranging internode lengths averaging 30.4 features exhibit strong quantitative overlap. ^ leaW , Throughout habit, much plant the geographical range of Croton variation in dioicus there is subshrub and and leaf internode woody-based size (Fig. In growth form plants range from low, ^ 1). new eventua y erect growth, that to plants that die back to the base and produce erect-ascending shoots ar£* and are give rise to upright lateral shoots during the growth season. In most plants the basal leaves ^ and ranges t the terminal, younger shape leaves are progressively smaller and often narrower. Leaf and broadly ovate, elliptical, oblong-ovate, linear-lanceolate, oblong-elliptic, oblong-lanceolate, from central Texas and large-size northeastern Mexico have more moderate- to broader, ovate, , 297 bigbendensis revisited Croton Henrkkson, Croton dioicus trans-Pecos Texas • cis-Pecos Texas Mexico * mm) Maximum intemode length (in ^IMeans intemode ofeach specimen annotated and the longest and standard deviations of measurements taken ofthe longest leaf (length, width, and lenght/width ratio) ^ dioicus specimens are combinedfor the *T*gbendensisT by Turner, and each specimen of Croton dioicus from trans-Pecos Texas, cis-Pecos Texas, and Mexico. All C. standard deviation of"dioicus all collections". Intemode length Lf.iyw ratio Lfwidth-mm count Lflength-mm ±193 ± ^bendensis* 50.0 353 ± 63 ±2.0 5.9 2.4 41 10.0 32.0± 112 ±0.8 ^s-trans-Pecos 3.4 ±2.1 72 7.7 ±102 293 ± 32 tfoicus-cjs-Pecos ±53 ±2.2 0.9 98 7 7 23.4 ±11.4 j!0 ±1.5 30.4 'cu$-Mexico 3.8 ±12 ±10.9 33 30.4 collections 255 ±6.4 24.5 may good they years of rainfall Of but in desert more numerous, smaller leaves, habitats often have Texas trans-Pecos are Urge of C. dioicus in leaves and strong terminal growth. Overall, the leaves “bigbendensis.” ^•elliptical those of very similar to to otherwise elliptical ovate but are based Pecos Texas Uglue in trans- 2 shows and “bigbendensis" the distribution of plants of Croton dioicus and well differentiated by solid circles indicated annotated by Turner Croton dioicus is (2004). and shown open the as circles, intemodes) are long and/or a. e those with narrower leaves . Figure are T** 01 Ihose by Turner, but nested withC. dioicus in 1, specimens "bigbendensis" annotated as growing two shows the taxa as open map from that of Turner (2004) it *>y squares. This differs 299 mm maximum had narrow leaves with 1/w ratios of 3.9-6.3, but internodes 27-55 in length. Puebla also from specimens from Nuevo Leon, also compare well with the proposed “bigbendensis,” Urbatsch 1019 Some e.g., mm, with internodes to 41 leaves 37 x 5.2, (1/w ratio showing that the characteristics used by (TEX), 7.1), establish his new taxon were by no means restricted to the Big Bend area of Texas. Turner to was growth Most The one characteristic that not possible to analyze is that of habit. Croton dioicus in woody suffrutescent-suffruticose, at the base, with herbaceous stems above forming bushes to about Texas is 2-3 dm with the size reflecting water resources of the season. Plants of “bigbendensis” are typically tall, Turner (2004) notes the hight of “bigbendensis” as 4-5 dm. However, Lott et al. 5588 [Presidio Co., larger. m Texas (TEX)] notes growth habit as a single-stemmed shrub to 1 tall, Turner 24-351 [Hudspeth Co. Texas m (TEX)] includes a photograph of a bushy plant ca. 1 tall and wide. 1 have seen plants in the foothills of Chianti Mts. (Presidio Co., Texas) with long lax stems that are initially erect but that eventually fall over the dm dm and produce erect sucker shoots to form low rounded plants about 3 tall but 12 in diameter. Regarding substrate, most of the specimens of “bigbendensis” are from sandy or otherwise well drained soils, but others are from clay-limestone flats and hillsides and still others are from roadsides etc. Label data is missing o specimens c e soil t » several collections fi : Brewster Co.,Texas that were noted coming from clay or limestone substrates-hillsides. flats, Two collections made by Turner in 2004 in gypsum soils in northeastern Culberson County, Texas 24-409 (TEX) (Fig 2) illustrate the problem with Turner’s interpretation of the taxon. Turner is a pistillate mm x with rounded 26.5 8.2 (1/w ratio plant considered to be C. dioicus that has oblong-ovate leaves tips, mm 24-402 (TEX) and intemodes 42 growing with/near a staminate specimen (Turner 3.2) to long. ) is It mm mm with internodes to 46 long that that has lanceolate, acute-tipped 31 x 6.5 (1/w ratio 4.7) leaves, and both are coloration is identified as “bigbendensis.” The two specimens appear identical in stature, etc. m normal range flower. But while the specimen he considers to be “bigbendensis” is well out of its (Fig. 2), no the specimen by Turner “growing with C. bigbendensis (24-402); of C. dioicus bears a hand-written note intermediates seen.” see this as just variation within a population of C. dioicus. 1 Turner 2004) advocates the Turner 2003; Turner’s Species Concepts Turner Turner 2001; et al. (in : logical species concept implying that his species have some degree of biological (i.e., reproductive) isola- importance he speaks of the tion sensu Mayr same personal discussions, 1969, 1992. At the time, in his recognition Turner 2001) in species tto-geo-naorphologic morpho-eco-geographic integerity, al factors (or (gypsum, “which types may or in different soil species occur in different habitats, differ ecologically i.e., combina- »nd) or be have some morphological discontinuity or a geographically and/or isolated (disjunct) with subspecies reserved only for of these taxa variety, features. His primary rank infraspecific is for Nesom He and dustering and Turner (2000). Holmgren groups of varieties the need arises sensu (1994) if ^ morphologically and generally that geographically separate varieties are subunits of a species that are be dlst with related taxa to varieties: if inguishable, must show intergradation but in Turner’s concept they kseesno (Henrickson 2004). intergradation, they considered distinct species are He considers The where Turner departs from others. concept that must show intergradation is varieties “s used minor varients modem where varieties are for interpretation as Old-School definitions in contrast to ofa say that But think safe to ~species as defined in Correll and Johnston (1970) and Diggs et al. (1999). I it is m L have geographical a subunits of a species that today as recognize subspecies) varieties (or > And then ^PonentfStue: presence or absence of intergradation. the without such regard to t be recognized needs species to 15 wide-ranging found in separate question whether variation of all many new species. ^laturally. why he publishes so But does explain Turner’s concept varietal m penphera and that 11 “expected some degree of variation, exhibit that outbreeding species will all environmental ^“tions, new or abiotic any biotic adapted to selection would individuals best favor those environment. In current Over move toward adaptation to their time, populations tend to all way, by genetic drift (Grant non-adaptive sometimes in a 0115 these chan can be enhanced es fiTv^ S ’ , 1%3 )-Ifthek or in moi! e availabili Nation substrate in I of an outlying population differs ^ new expect changes reflecting adaptation to this environment. But even if adaptive characteristics become make fixed in an outlying population, does this the population a distinct species? and In this particular instance, Croton dioicus of northern trans-Pecos adjacent portions of central Texas mostly occurs in clay flats in which much of the rainfall runs off quickly, and the plants tend to be short, low rounded specimens adapted to a seasonally severe environment. In areas of sandy-gravelly substrates, the water can penetrate deeply, providing a reservoir of water for later development. Rhyolitic substrates can form coarse gravels-sands that also accumulate rainwaters. Other sandy habitats in this region occur along An the Rio Grande. increase in moisture availability would favor those plants that could grow larger and produced more flowers and fruits over a season. This would not require any novel gene-based changes, bot rather would simply favor those plants within a population that produce more growth-regulating substances (auxins etc.) that would in turn promote more robust plants with longer internodes and steins and leaves, would characteristics that not be adaptive in drier Since the southern portion of the southwestern sites. trans-Pecos Texas has volcanic (not limestone) mountains, and has other sandy habitats along the Rio Grande, the sandy-gravelly habitats tend to be geographically separated. With Turner’s eco-geo-morphological concept, he finds ecological, geographic and morphological dif- new ferences between the clay- vs. sandy-substrate populations. But he notes that his species is a biological map own specimens isolation. His (Turner 2004) shows the two taxa as completely allopatric, but using his mapped as here in figure 2 (some added after his publication), they are not completely allopatric except in the sands along the Rio Grande in Presidio Co., Texas. What we populations in well are dealing with in “bigbendensis,” appears be a derivative series of to In drained soils that differ only in quantitative characteristics from those on primarily clay substrates. C widespread characteristics of vestiture, flower, and and time of anthesis, they are identical to the fruit, values dioicus. Quantitative characters can be used to establish species there are no or reduced overlapping if (Luckow But shown merge with those of C. dioicus 1995). as in Fig. the values of C. “bigbendensis” strongly 1, o making my measurements of 10 recognition As at the species rank, in opinion, untenable. noted above, the 41 specimens recognized by Turner as “bigbendensis” are nested well within the specimens of C. dioicus “bigbendensis and and (Fig. 2) others are closely peripheral. Even these were to be considered C. dioicus if would were redefined as only those plants with longer internodes and/or narrower leaves, “bigbendensis" internodes, still consist of an amalgamation of plants, some with narrower leaves and others with longer would that not from separate the variation in C. dioicus. good raii& There of is another problem associated with such quantitatively defined “taxa.” In times the plants can show strong growth with long leaves and internodes. But under poor growth conditions, may wlthin plants be stunted with shorter internodes and smaller leaves and some of the plants nested _ broad* may dioicus in figure 2 be growth season are typically just that. Also, the first-formed leaves of a than those formed later in the season. in internodes But while the data do show the existence of plants with narrower leaves and longer Due t0 southern margin of trans-Pecos Texas, the plants are not clearly distinguished from C. dioicus. 0* own blending of the criteria quantitative characteristics used to define “bigbendensis,” using Turner’s and Nesom rec0gI no reason to 2000), the taxon would be considered see ^ a variety of C. dioicus. But, I ranging wide bigbendensis” at any rank, but to incorporate characters into the known variation of the it’s ^ recognize ^ poorly studied As Croton easily dioicus. stands, Croton very species, it dioicus is a distinctive m range by differ its substantial characters. see no value in recognize peripherial populations that I e “bigben quantitative characters as equal no evidence that species. Certainly in this instance there is expen good is a biological species. But we must remember without even with observations, that field data, such taxonomic decisions are just opinion.