**Senecio vulgaris L. (Asteraceae)**

**Common Groundsel**

**Description**. Annual, herbaceous, from a thin, branched taproot;
stems 8-60 cm tall, erect to decumbent, somewhat succulent, sparsely
tomentose when young, glabrous to sparsely villous, simple or branched
near the base. Leaves 2-5(10) cm long, 0.5-4.5 cm wide, deeply pinnately
lobed or toothed, glabrous to sparsely villous, the lobes oblong,
irregularly toothed, the lower ones petioled, oblanceolate to obovate,
base abruptly tapered, the upper ones oblong, sessile or clasping, the
bases sometimes auriculate. Heads discoid (all corollas radial and
salverform), 5-10 mm long, 4-10 mm wide, cylindrical to subcylindrical,
subsessile to stalked, 8-20, in terminal or axillary clusters.
Phyllaries in two series, glabrous to sparsely pubescent, green,
black-tipped, the outer ones 2-10, 1-2 mm long, the inner ones 21, 4-6
mm long, linear-lanceolate, margins scarious, apices acute, glabrous to
loosely tomentose. Corollas yellow. Achenes 1.5-2 mm long, brown,
glabrous or with appressed-puberulent ribs; pappus 15-20 mm long,
simple, white. In California, flowering from January through December.
(Barkley 1993, Chater and Walters 1976, Clapham et al. 1962, Cronquist
1980, 1994, Fernald 1950, Great Plains Flora Association 1986, Munz
1959, Welsh et al. 1987).

*Senecio vulgaris* is a polyploid (2n=40), believed to have been derived
through hybridization involving at least one extant species, *S.
squalidus* L. (Ashton and Abbott 1992, Harris 1992, Stace 1977).
Introgressive hybridization from *S. squalidus* has contributed to
genetic variability in European populations (Abbott et al. 1992),
including forms with ray flowers (Abbott et al. 1990, Ingram and Noltie
1984, Ingram et al. 1980). Such races are not apparently present in
introduced populations, at least in California as inferred from
descriptions in Barkley (1993) and Munz (1959). Naturalized British
populations show considerable genetic variation (Theaker and Briggs
1992, 1993). Genetic variation included the evolution of strains with
varying growth rates, this in response to natural selection imposed by
weed removal methods (Kadereit and Briggs 1985, Theaker and Briggs
1993).

**Geographic distribution**. Native and widespread throughout
continental Europe, but more common in the Mediterranean region. It has
been introduced into Australia, New Zealand, throughout North America,
Great Britain \[repeatedley according to Stace (1997) and Ingram et al.
1980)\], Japan, southern Africa (Arnold and de Wet 1993, Chater and
Walters 1976, Clapham et al. 1962, Cronquist 1980, 1994, Fernald 1950,
Ohwi 1953, Webb et al. 1988).

Common groundsel was first reported from California ("near San
Francisco") in 1876 (Brewer et al. 1876). Naturalized populations occur
on all the Channel Islands except for Santa Barbara (Junak et al. 1995),
coastal California from Del Norte County southward to San Diego County,
and in most counties west of the Sierra Nevada (Anonymous 1998, Barkley
1993).

**Ecological distribution**. In its natural range, common groundsel
occurs in cultivated and fallow fields (Chater and Walters 1976, Clapham
et al. 1962). It has been reported elsewhere from similar habitats
(e.g., (Barkley 1993, Fernald 1950, Munz 1959, Welsh et al. 1987), in
turf (Murphy 1996), and in household gardens (Senesac 1991).

**Reproductive and vegetative biology**. Common groundsel is
self-compatible, but experiences some outcrossing in native populations
(Abbott et al. 1990, Marshall and Abbott 1984a, 1984b). Reproductive
capacity is high relative to total plant biomass (Harper and Ogden
1970). Small, light seeds and proportionately large pappus confer a
relatively high level of dispersability (Anderson 1992, Sheldon and
Burrows 1973)

In Britain, common groundsel seeds may germinate at any time of the
year, depending on availability of water (Harper and Ogden 1970). Most
plants live for about 3 months; flowering and reproduction begins within
6-8 weeks. A comparison of strains from wild Scotish and Spanish
populations demonstrated differences in the proportion of dormant seeds
and rates of germination, which were related to differences between
cold- and warm-temperate (Mediterranean) climates (Ren and Abbott 1991).
In general, seeds of cold-temperate strains do not germinate unless they
have been exposed to freezing temperatures; those of warm-temperate
(Mediterranean) climates display little dormancy, germinating only after
sufficient precipitation. However, buried seeds may remain viable and
dormant for as long as 5 years (Roberts 1964).

Using experimental populations differing in patchiness and density,
Bergelson (1990) demonstrated that establishment and reproductive
capacity was greater when competing species (i.e., *Poa annua*) were
clumped rather than randomly distributed; this suggests that common
groundsel may not be competitive under conditions of relatively dense
cover (Bergelson et al. 1993). This is consistent with observations that
common groundsel is invasive and common in disturbed habitats (Harper
and Ogden 1970, Murphy 1996, Senesac 1991), and does not compete well
under horticultural practices that minimize open space (Qasem and Hill
1993). Common groundsel also has been reported as invasive after fires,
both in European shrubland (Trabaud 1991) and in California chasparral
(Sweeney 1956, Biswell 1974). However, in both instances, it does not
persist except in disturbed sites.

Allelopathy (Qasem and Hill 1989), nitrogen levels (Qasem and Hill
1993), and both intra- and inter-specific interactions among seedlings
(Bergelson and Perry 1989) have been implicated as factors conferring
competitive advantage to persistence in naturalized populations.

**Weed status**. Common groundsel is not considered a serious noxious
weed in agricultural or horticultural practice, at least at a global
level (not listed by Holm et al. 1977), nor is it considered a noxious
weed by the State Dept. of Food and Agriculture (Anonymous 1996).
However, it has been reported as weedy and invasive, primarily in
disturbed sites, fallow or cultivated (both agricultural and
horticultural) fields, in turf, and in urban gardens, where it is able
to germinate and grow at any time the year (Murphy 1996, Senesac 1991).

**Microbial pathogens.** Several studies have investigated natural
fungal pathogens (Ayres 1995, Baka and Losel 1992, Hallett et al. 1990a,
1990b, Hallett and Ayres 1992, Harry and Clarke 1992, Paul 1989, Paul
and Ayers 1987b, 1990, Preese 1987), which include mildews (*Albugo*
spp., *Botrytis* spp., *Erysiphe fischeri*, *E. cichoracearum*,
*Sphaerotheca epilobii*) and rusts (*Puccinia lagenophorae*, *P.
punctiformis*, *Uromyces* spp.). Most of these studies, however, are
based on greenhouse conditions or in horticultural (e.g., flowers) and
agricultural production (e.g., lettuce).

Application of fungal diseases to biocontrol of *Senecio vulgaris* has
been discussed by Paul et al. (1993). Damage by *Puccinia lagenophorae*
is enhanced by mild drought conditions, periods of frost in winter, and
by competition between groundsel and neighbouring plants, but is reduced
by nutrient deficiency. Rust injury also is greatly increased by
secondary infection of pustules by necrotrophic fungi. Other
interactions that influence survival include the extent of mycorrhizal
infection and phosphate levels in the soil (West 1995a, West 1995b),
availability and composition of nutrients (Paul and Ayres 1986a, Paul
and Ayres 1990), season of infestation (Paul and Ayres 1986c, Paul and
Ayres 1986d, Paul and Ayres 1986e, Paul and Ayres 1987a), and intra- or
inter-specific competition (Paul and Ayres 1986b, Paul and Ayres 1987b,
Paul and Ayres 1990). A few studies have shown that *Senecio vulgaris*
can evolve fungal-resistant strains (Harry and Clarke 1986, 1987).

**Insect pathogens.** No literature that reported common groundsel as a
host of insect pathogens was found. Common groundsel produces
pyrrolizidine alkaloids (e.g., Hartmann and M. Zimmer, 1986. Pieters and
Vlietinck 1988), which are known to be either toxic (McHenry et al.
1990, Mitich 1995) or distasteful (Blaney and Simmonds 1985) to
potential herbivores.

**Herbicide control.** The effectiveness of over 10 different herbicides
(e.g., metolachlor, acifluorfen, simazine) on groundsel were tested
(Al-Khatib 1995, Gallitano and Skroch 1993, Sym 1988), but primarily in
association with agricultural crops or container propagation. Several
studies studied various levels of resistance to such herbicides as
atrazine, simazine, and triazine (Delaney 1984, Derr 1991, Fuerst et al.
1986, Havaux 1989, McCloskey and Holt 1990, 1991, Stephenson et al.
1990, Watson et al. 1987). Watson et al. (1987) provided evidence for
relatively simple inheritance (a few loci) for herbicide resistance.
Stowe and Holt (1988) examined physological mechanisms that confer
herbicide resistance by comparing triazine-resistant, non-resistant, and
hybrid strains. Holt and Goffner (1985) studied morphological and
physiological traits associated with simazine resistance.

Relatively rapid selection for genetic strains differing in cultural
conditions, minor morphological traits, and herbicide resistance has
been demonstrated in some populations (Briggs and Block 1992, Briggs et
al. 1992, Radosevich 1973). Holliday and Putwain (1977, 1980) showed
that recruitment of simazine-resistant strains came from resident seed
banks, rather than from immigration seeds, because resident strains
germinated, survived, and reproduced during times coincident with low
herbicide levels.

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