Flora of North America species comparison

Genera ca. 100, species ca. 2000 (27 genera, 292 species in the flora).

Orobanchaceae are now defined to include both the holoparasitic members traditionally included in the family (A. Cronquist 1981) and the hemiparasitic genera formerly included in Scrophulariaceae. Although multiple research groups focus on members of the Orobanchaceae, a widely accepted infrafamilial classification of the family in the sense of Angiosperm Phylogeny Group (2016) has not yet appeared.

The classification by J. R. McNeal et al. (2013), who found that Orobanchaceae comprise six clades, is followed herein (their named clades are roughly equivalent to tribes). The autotrophic Lindenbergia Lehmann (12 species in the Old World) corresponds to the basal clade sister to the rest of the clades. Species in our region are distributed among the remaining five clades: Cymbarieae D. Don (genus 1), Orobancheae Lamarck & de Candolle (genera 2–6), Rhinantheae Lamarck & de Candolle (genera 7–12), Buchnereae Bentham (genera 13 and 14), and Pedicularideae Duby (genera 15–27). Within the family, genera are arranged alphabetically within tribes, or within Pedicularideae, in subgroups within the tribe.

Parasitic plants attach to their hosts via haustoria (L. J. Irving and D. D. Cameron 2009). Haustoria are produced by both hemiparasitic and holoparasitic Orobanchaceae (E. Fischer 2004). In hemiparasitic taxa, haustoria usually tap their host’s xylem, mostly taking up water, mineral nutrients, and nitrogen from their host, and sometimes also carbon. Holoparasitic taxa derive all of their growth requirements predominantly from the host’s phloem (Irving and Cameron).

Parasitism has evolved once in the family (N. D. Young et al. 1999; J. R. McNeal et al. 2013); holoparasitism has arisen independently three times from the hemiparasitic condition (J. R. Bennett and S. Mathews 2006; McNeal et al.).

Some Orobanchaceae are serious pests, primarily on legume and grain crops in warmer and drier areas, especially in sub-Saharan Africa. Striga is a particularly serious pest that parasitizes mostly monocots; S. gesnerioides attacks eudicots (K. I. Mohamed et al. 2006). Orobanche parasitizes eudicot crops primarily in temperate parts of the world (E. S. Teryokhin 1997). All Striga species and non-native species of Orobanche in the flora area are listed on the Federal Noxious Weed List (http://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/weedlist.pdf) in the United States.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species 400–600 (37 in the flora).

E. Hultén (1968) listed three Pedicularis taxa in his Flora of Alaska and Neighboring Territories that do not occur in the flora area; P. amoena Adams ex Steven, P. kanei Durand subsp. adamsii (Hultén) Hultén, and P. villosa Ledebour ex Sprengel are found on the Chukchi Peninsula of Siberia.

The most common chromosome number for Pedicularis is 2n = 16. Two species are reported to have a diploid number of 2n = 12, and at least five species have a number of 2n = 14. See reviews in Jie C. et al. (2004) and M. I. S. Saggoo and D. K. Srivastava (2009).

Infrageneric classification of Pedicularis is both difficult and incomplete. The author has not attempted to present one for the North American taxa. Inconsistencies result from using either floral morphology or phyllotaxy to construct major subgeneric groups (C. Steven 1823; G. Bentham 1835; C. J. Maximowicz 1888; D. Prain 1890; G. Bonati 1918; Tsoong P. C. 1955); the latter author proposed 130 series to accommodate the worldwide variation in Pedicularis. Recognizing that floral form probably evolved in parallel among groups, Li H. L. (1948) employed phyllotaxy to erect three informal subgeneric taxa (greges) for the Pedicularis of China, including grex Allophyllum, species with alternate leaves; grex Cyclophyllum, species with opposite or verticillate arrangement of leaves; and grex Poecilophyllum, species with alternate to subopposite leaves on the same plant. However, molecular phylogenies (Yang F. S. et al. 2003; R. H. Ree 2005; B. W. Robart et al. 2015; Yu W. B. et al. 2015) indicate inconsistencies even in the treatment by Li, although the study by Yu et al., which included 257 species, did show that grex Cyclophyllum is monophyletic.

Pediculariopsis was described to account for species (for example, Pedicularis verticillata) that exhibit a different base chromosome number (x = 6 versus x = 8). That concept has not been accepted by others, because there is little morphological support.

The use of infraspecific ranks in Pedicularis follows T. F. Stuessy (1990), who argued that the subspecific rank is appropriate when several obvious morphological differences are associated with an allopatric or peripatric geographical pattern, whereas the varietal rank is appropriate when one to few differences are associated with more or less geographic overlap. Unfortunately, Pedicularis specialists have not used these levels consistently. The subspecies rank is used here, except in P. bracteosa, P. centranthera, and P. contorta.

Pedicularis is a common element of arctic and alpine habitats in the Northern Hemisphere, with the greatest concentration of species occurring in Asia.

Etymology: Latin pediculus, louse, alluding to belief that livestock feeding on P. palustris developed lice

(Discussion copyrighted by Flora of North America; reprinted with permission.)