A taxonomic evaluation of Astrophytum myriostigma var. nudum (Cactaceae)

  • Richard R. Montanucci Department of Biological Sciences, Clemson University
  • Klaus-Peter Kleszewski

Abstract

The absence of epidermal trichomes has been used as a diagnostic character to distinguish Astrophytum myriostigma var. nudum from other infraspecific taxa. In the Huizache region of San Luis Potosi, Mexico, between the elevations of 1320 m and 1700 m, the local populations of A. myriostigma are polymorphic, comprised of nude, semi-nude, and flecked plants. However, this polymorphism is non-discrete as there is considerable variation and intermediacy among plants. Also, the proportion of nude plants increases gradually with elevation, which suggests clinal variation correlated with altitude. Exclusively nude populations are currently known only from near Santa Rita del Rucio (? 1710 m) and south of Entronque Huizache (? 1750 m). Farther south, flecked plants were recorded at 1726 m elevation at 6 km E of Guadalcazar, and to the north near El Realejo flecked plants occur as high as 1920 m. At localities southeast of the Sierra San Pedro (Sierra Guadalcazar), nude and semi-nude plants are absent or present at relatively low frequencies in local populations.

Epidermal trichomes provide shading and reflectance that protects the cactus stem against excessive solar radiation and moderates stem temperature. The majority of nude A. myriostigma growing in exposed locations at the margins of Hechtia colonies were found to suffer from chlorophyll degeneration due to excessive exposure to solar radiation.

A comparative morphological study did not find any characters which can be used in combination to diagnose the var. nudum. Given the lack of a suite of discrete, or nearly discrete diagnostic characters, and given that exclusively nude populations do not have a definable geographic distribution we suggest that the nude phenotype should be treated taxonomically as a “form” rather than as a geographical “variety,” or subspecies. 

References

Backeberg, C. 1961. Die Cactaceae. Vol. 5. VEB Gustav Fischer Verlag, Jena, Germany.

du Rietz, G.E. 1930. The fundamental units of biological taxonomy. Svensk Bot. Tidskr. 24:333–428.

Eggli, U. 1985. Backeberg’s invalid cactus names. Bradleya 3:97–102.

Gibson, A.C. & P.S. Nobel. 1986. The cactus primer. Harvard University Press, Cambridge, MA, U.S.A.

González-M., F. 2004. Las comunidades vegetales de México: Propuesta para la unificación de la clasificación y nomenclatura de la vegetación de México. Instituto Nacional de Ecología. Semarnat. México, D.F., México.

Hoock, H. & K.P. Kleszewski. 2004. Wuchsort in exponierten Höhenlagen: Astrophytum myriostigma var. nudum (R. Meyer) Megata. Kakteen And. Sukk. 55(2):29–34.

Hoock, H. 1993. Entdeckt, verloren, wiedergefunden: Astrophytum myriostigma Lemaire bei der Mine von San Rafael, San Luis Potosí. Kakteen And. Sukk. 44(10):212–215.

Hoock, H. 2008. Astrophytum Lem. (Cactaceae). Schoendruck-media e. K., Landshut, Germany.

Jurado, E., J. Flores, G. Muro Pérez, H. González Rodríguez, M. Pando Moreno, & O. Doria. 2013. Are nurse plants always necessary for succulent plants? Observations in northeastern Mexico, including endangered and threatened species. Bradleya 31:150–156.

Kleszewski, K.P. 1994. Begegnungen mit Astrophyten an der Huizache-Kreuzung. Kaktusblüte 11:48–51.

Lux, A. & R. Kopunec. 1992. Gaseous and liquid phase water uptake by the stem surface of Astrophytum (Cactaceae). Environm. Exp. Bot. 32(1):75–81.

Mabry, T.J. & A.S. Dreiding. 1968. The betalains. In: T.J. Mabry, R.E. Alston, & V.C. Runeckles, eds. Recent advances in phytochemistry. Appleton-Century-Crofts, New York, NY, U.S.A. 1:145–60.

Medellín-L., F. 1982. The Chihuahuan Desert. In: G.L. Bender, ed. Reference handbook on the deserts of North America. Greenwood Press, Westport, CT, U.S.A.

Megata, M. 1944. An account of the genus Astrophytum Lemaire. Mem. Coll. Agric. Kyoto Imp. Univ. 56:1–62, 10 plates.

Meyer, R. 1912. Echinocactus myriostigma S.-D. var. nuda R. Mey. var. nov. Monatsschr. Kakteenk. 22(9):136–137.

Meyer, R. 1913. Kleine Mitteilungen. Monatsschr. Kakteenk. 23(12):191.

Montanucc i, R.R. & K.P. Kleszewski. 2019. Nomenclature and redescription of the Jaumave Valley populations of Astrophytum myriostigma (Cactaceae). J. Bot. Res. Inst. Texas 13(1):63–69.

Nobel, P.S. 1978. Surface temperatures of cacti-influences of environmental and morphological factors. Ecology 59:986–996.

Nobel, P.S. 1988. Environmental biology of agaves and cacti. Cambridge University Press, Cambridge, UK.

Okumura, Y. 1933. Classification of Astrophytum. Stud. Cacti (Osaka) 4:174–175, 195–201, 215–216.

Sadovský, O. & B. Sch ütz. 1979. Die Gattung Astrophytum. Arten. Hybriden. Kultur. Flora-Verlag, Titisee-Neustadt, Germany.

Stace, C. 1989. Plant taxonomy and biosystematics. 2nd ed. Edward Arnold, London, UK.

Stebbins, Jr., G.L. 1950. Variation and evolution in plants. Columbia University Press, New York, NY, U.S.A.

Stuessy, T.F. 1990. Plant taxonomy: The systematic evaluation of comparative data. Columbia University Press, New York, NY, U.S.A.

Viereck, H.W. 1939. Astrophyten, wie sie der Sammler in den Heimatgebieten sieht. Beit. Sukkulentenk. Sukkulentenpflege (1):4–8.

Published
2020-12-07
How to Cite
Montanucci, R. R., & Kleszewski, K.-P. (2020). A taxonomic evaluation of Astrophytum myriostigma var. nudum (Cactaceae). Journal of the Botanical Research Institute of Texas, 14(2), 255-264. https://doi.org/10.17348/jbrit.v14.i2.1006