Orobanche ramosa
Sp. Pl. 2: 633. 1753.
Plants few- to many-branched, (5–)10–45 cm, slender, base usually only slightly enlarged. Roots often inconspicuous (sometimes forming a globose mass), very slender, usually branched. Leaves relatively few, not imbricate, appressed to loosely ascending or spreading; blade lanceolate to narrowly ovate, 4–7 mm, margins entire, apex acute, surfaces glandular-pubescent or glabrous. Inflorescences spikes or spikelike racemes, pale tan to yellow or brownish purple, sometimes with a brownish cast, simple, densely glandular-pubescent; flowers numerous; bracts ± ascending, lanceolate, 4–6 mm, apex acute, glandular-pubescent. Pedicels 0–1 mm; bracteoles 2. Flowers: calyx purple or yellow, sometimes brownish, bilaterally symmetric, 4.5–6.5 mm, divided into 4 subequal lobes, lobes triangular-acuminate, entire, glandular-pubescent; corolla 10–15(–17) mm, tube white or light purple to bluish purple, slightly constricted above ovary, slightly to moderately curved forward, glandular-pubescent; palatal folds prominent, white, pubescent; lips similar in color to tube or slightly darker purple to bluish purple, sometimes with ± darker veins (these often externally darker), abaxial lip slightly reflexed, 3–5 mm, lobes oblong-ovate, apex rounded to bluntly pointed, adaxial lip usually spreading to ± recurved near tip, 3–5 mm, lobes broadly ovate to semiorbiculate, apex rounded to bluntly pointed; filaments glabrous or sparsely glandular-pubescent, anthers included, glabrous or nearly so. Capsules broadly ovoid to broadly oblong-ellipsoid, 5–9 mm. Seeds 0.2–0.5 mm. 2n = 24.
Phenology: Flowering Feb–Apr, Jul–Sep.
Habitat: Roadsides, crop fields, lawns, disturbed areas, greenhouses.
Elevation: 0–300 m.
Distribution
Introduced; Calif., Ill., Ky., N.J., Tex., Va., Eurasia, Africa
Discussion
The identity of the sole historical collection of Orobanche ramosa from North Carolina (Roan Mtn., J. Ball s.n., 17 September 1884, E) remains tentative (L. J. Musselman 1984). Many other historic infestations of this weedy species in the region have been eradicated. However, in recent decades the species appears to be spreading in central and eastern Texas using disturbed roadsides as avenues for dispersal.
This destructive agricultural weed has a large host range. L. J. Musselman and K. C. Nixon (1981) documented plants within a single population in Texas attached to the roots of ten different hosts in eight angiosperm families: Apiaceae, Asteraceae, Caryophyllaceae, Fabaceae, Geraniaceae, Malvaceae, Onagraceae, and Verbenaceae. Other voucher specimens have recorded an even more diverse assemblage of hosts, mainly eudicots and occasionally even monocots. Historically, the principal crop species affected in the region have been hemp, tobacco, and tomato, but an infestation in a commercial greenhouse in New York impacted coleus (Plectranthus) production in the 1920s. Currently, the main negative economic impact of Orobanche ramosa is in tomato fields in California.
As many as 20 microspecies have been described as segregates from Orobanche ramosa (F. J. Rumsey and S. L. Jury 1991). However, A. O. Chater and D. A. Webb (1972), who chose to circumscribe O. ramosa broadly as a single species with three subspecies, noted that the characters used to discriminate among these taxa exhibit nearly continuous variation and are often quite variable within populations. In their treatment, subsp. ramosa is the widespread weedy taxon that has emigrated to the New World, and the other two infrataxa [subsp. mutelii (F. J. Schultz) Coutinho and subsp. nana (Reuter) Coutinho] are uncommon, non-weedy taxa endemic to southern Europe that differ from subsp. ramosa in perianth details. Further studies are needed before an infraspecific classification can be supported.
As noted by H. J. Scoggan (1978–1979), Orobanche purpurea Jacquin (yarrow broomrape), was collected in Huron County, Ontario, in 1895 by Jasi A. Morton but has not been rediscovered in the flora area since the initial collection. The voucher specimens lack habitat data, but in its native range the species parasitizes mainly open grassland and woodland taxa of Achillea and Artemisia (Asteraceae). The species resembles O. ramosa, differing in its usually simple stems, longer corollas (18–25 mm), and calyces with slightly longer, more narrowly triangular lobes. Although its native distribution in Europe, Asia, and northern Africa is broad, C. A. J. Kreutz (1995) noted that it is rare in much of the range, and F. J. Rumsey and S. L. Jury (1991) were alarmed at its historical decline in Great Britain.
Selected References
None.