Dahlia spectabilis

 

Dahlia spectabilis D.E. Saar & P.D. Sørensen was discovered during a collecting trip in 2005 east of Zaragoza along a gravel road to Salitrera, in the Mexican state of San Luis Potosí (Saar, 1999). The specific epithet, spectabilis, was chosen to reflect the fact that these are large and showy plants (Saar et al., 2002). The only population observed was growing in an arid zone of mimosoid scrub (bean family with Mimosa-like flowers), arborescent Opuntia (tree-like/size cactus), and large Agave (includes Century Plant and others with similar habit). The plants were growing along the top edge of an ENE-facing dry clay roadcut at an elevation of 2,030 meters (6,660 feet). Agave, Opuntia, and other tough and spiny plants surrounded the dahlias and formed a living fence that protected them from grazing animals. After finding the original population, J. P. Hjerting, P. D. Sørensen, and D. E. Saar searched east of the original locality to Salitrera, in hopes of locating additional populations, but much of the countryside was heavily grazed and no other plants were located. Heavy grazing has severely degraded many areas of Mexico (e.g., Bacon & Saar, 2007).

D. spectabilis is an herbaceous perennial from tubers, with one or more stems that can reach a height of 2.4 m (7.9’). Stems are glaucous and nearly round to slightly angled. Median leaves are 27-35 cm (10.6-13.8”) long (including petioles), twice compound, and frequently with stipels at the first (lowest) and/or second rachis node; blade margin teeth are glabrous (vs. ciliolate). The flower head is up to 14.5 cm (5.7”) across, which is the largest of any species in the genus except D. campanulat. The disc florets of D. spectabilis are yellow and fertile; the 7-8 ray florets are sterile, 5.8-7 cm (2.3-2.8”) long x 2.1-3.2 cm (0.8-1.3”) wide, and light lavender with darker colored longitudinal veins on the abaxial (lower) surface. Flowering occurs from August through at least October (Saar et al., 2002). Although this is a relatively large, albeit herbaceous, species, molecular data indicate it is not closely related to other large species, such as D. excela, D. imperialis, and D. teniucaulis. D. spectabilis occurs in a separate clade than the three aforementioned species, and is more closely allied with species such as D. scapigera and D. pteropoda (Saar et al., 2003).

 

This species has 64 chromosomes per cell.

 

References:

 

Bacon, J.R. and D.E. Saar. 2007. Investigando el Flor de México. Universale Forestum 6: 12-14. [in Spanish]

 

Saar, D.E. 1999. A phylogenetic analysis of the genus Dahlia (Asteraceae): an interdisciplinary study. Ph.D. dissertation, Department of Biological Sciences, Northern Illinois University, DeKalb, IL, USA, 266pp.

 

Saar, D.E., P.D. Sørensen, and J.P. Hjerting. 2002 Dahlia spectabilis (Asteraceae): a new species from San Louis Potosí, Mexico. Brittonia 54: 116-119.

 

Saar, D.E., N.O. Polans, and P.D. Sørensen. 2003. A phylogenetic analysis of the genus Dahlia (Asteraceae) based on internal and external transcribed spacer regions of nuclear ribosomal DNA. Systematic Botany 28: 627-639.