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TABLE 2. Invasive lineages that evolved after intertaxon hybridization

Parent taxa

Family

Habit of hybrid lineage

Site of new lineage's origin

Evidence beyond morphology

Avena barbata* × A. strigosa*

Poaceae

Annual herb

North America

i

Beta vulgaris spp. vulgaris* × B. v. spp. maritima

Chenopodiaceae

Annual herb

Europe

n, o, b

Carpobrotus edulis* × C. chilense

Aizoaceae

Perennial herb

North America

as, i

Lythrum salicaria* × L. alatum

Lythraceae

Perennial herb

North America

d, s

Onopordum acanthium* × O. illyricum

Asteraceae

Perennial herb

Australia

n

Raphanus raphanistrum* × R. sativus*

Brassicaceae

Annual herb

North America

as, c, s

Rhododendron ponticum* × R. catawbiense*

Ericaceae

Shrub

Europe

n, o

Secale cereale* × S. montanum*

Poaceae

Perennial herb

North America

i, s

Spartina alterniflora* × S. foliosa

Poaceae

Perennial herb

North America

as, n, s

Viola riviniana × V. reichenbachiana

Violaceae

Perennial herb

Europe

c, n

as, Artificial synthesis; c, cytological; i, isozymes; n, nuclearDNA; o, organelle DNA; s, full or partial sterility.

* Signifies non-natives.

cite one or two good comprehensive references for each example. In many cases, the best reference is an article or review that cites many supporting sources of empirical research. To list each of those is beyond the scope of this paper. Finally, we present how the novel lineage is maintained and indicate the scope of its invasiveness, including whether the lineage is known to grow, at least in some instances, in human-disturbed areas.

Some characteristics of our sample seem to be quite broad; many diverse families are represented. Hybridity is stabilized by a variety of mechanisms, from cytological (polyploidy and permanent translocation heterozygosity) to apomictic (agamospermy and clonal growth). In many cases, the new hybrid lineage is a coalescent complex that absorbs one or both parental types, especially among the unnamed cases in Table 2. Likewise, invasiveness runs the gamut from cases in which the new hybrid lineage is displacing a parent or spreading into a new community to cases in which the hybrid lineage is an established noxious weed.

But we also note some interesting trends in our sample. Life history



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