**Capsella bursa-pastoris (L.) Medikus (Brassicaceae)**

**Shepherd's Purse**

**Description**. Annuals from slender taproots; stems 5-80 cm tall,
erect, simple or branched, somewhat angled or striate, pubescent below,
the trichomes stellate. Leaves alternate, lowermost ones in a basal
rosette, 3-15 cm long, oblanceolate in outline, slightly lobed to
pinnatifid, upper cauline leaves 2-6 cm long, lanceolate to oblong,
sessile, clasping, margins remotely toothed. Inflorescence a raceme;
petals 2-3 mm long, white; pedicels in fruit 7-15 mm long, spreading to
somewhat ascending, fruit a silicle, 4-9 mm long, 4-9 mm wide,
obcordate, strongly flattened perpendicular to the internal septum,
valve surfaces reticulate near the margins. Seeds several per locule,
ca. 1 mm in diameter, reddish brown, wingless. In California, flowering
from January to December. (Abrams 1944, Aksoy et al. 1998, Chater 1964,
Fernald 1950, Barker 1986, Munz 1959, Rollins 1993).

**Note:** Shepherd's purse is a tetraploid, believed derived from two
other species, *C*. *grandiflora* and *C*. *rubella,* and shows a broad
range of ecotypic variation and phenotypic plasticity for a number of
morphological and life history traits (Hurka and Neuffer 1997, Neuffer
1996, Neuffer and Albers 1996, Neuffer and Eschner 1995, Neuffer and
Meyer-Walf 1996).

**Geographic distribution**. A native of Europe, it is widespread
throughout the temperate world, including all continents and New Zealand
(Arnold and de Wet 1993, Hewson 1982, Holm et al. 1977, Lorenzi and
Jeffery 1987, Neuffer and Albers 1996, Rollins 1993, Tammaro and Giglio
1993-94).

Shepherd's purse is believed to have been introduced into California
sometime during the 19th century (Robbins 1940), although molecular
evidence suggests several introductions, with some presumably during the
Spanish period (Neuffer 1996). Naturalized populations occur on San
Clemente, San Miguel, Santa Catalina, Santa Cruz, and Santa Rosa islands
(Junak et al. 1995), and is reported from most counties west of the
Sierra Nevada (Anonymous 1998, Rollins 1993).

**Ecological distribution**. In its natural range, shepherd's purse
occurs in open sites, often in fallow fields, gardens, or abandoned
urban lots. It may occur in a wide array of habitats in the area of
naturalization, but commonly occurs in disturbed or recently cultivated
sites (Munz 1959, Robbins et al. 1970, Rollins 1993, Tammaro and Giglio
1993-94).

**Reproductive and vegetative biology**. Shepherd's purse reproduces
entirely by seeds. Like many small-flowered, annual mustards, shepherd's
purse is presumably self-compatible and largely self-pollinating,
although it does possess minute nectaries (Rollins 1993).

Seed dispersal presumably takes place through cultivation of
agricultural fields and contamination of soils under horticultural
conditions, although ground-dwelling beetles are reported to disperse
and bury seeds in northern Europe (Bernhardt, K-G. 1995). Conn and Deck
(1995) reported 2- 5 % viability in seeds that had been buried for
almost 10 years. Seed dormancy is generally broken by cool temperatures
followed by a light requirement (Popay and Roberts 1970a, 1970b,
Terpstra 1995), which may explain early spring germination in temperate
climates. Although often germinating in the fall or winter and fruiting
in the spring, it may become biennial in subtropical or warm-temperate
climates (Milbert and Andersson 1997). Alternatively, fluctuating
temperatures at higher levels (e.g., 25-30 degrees C), in combination
with certain solutes (e.g., nitrates or nitrites) also stimulates
germination, which may explain similar patterns of germination in
warm-temperate or subtropical climates (Neuffer and Koch 1996, Popay and
Roberts 1970a, 1970b).

Plants are capable of growing and reproducing throughout the year, given
sufficient moisture (Holm et al. 1977, Neuffer and Eschner 1995). Demars
and Boerner (1994) observed vescicular-arbuscular mycorrhizal infection
in a substantial portion of plants growing under urban conditions.

**Weed status**. Shepherd's purse is considered a noxious weed in
agricultural or horticultural practice, at least at a global level (Holm
et al. 1977), and in the United States (Lorenzi and Jeffrey 1987, but it
is not considered a noxious weed by the State Dept. of Food and
Agriculture (Anonymous 1996).

**Note**: Shepherd's purse has been considered a potential crop plant in
some parts of the world (e.g., Guil Guerrero and Torija Isasa. 1997,
Yang et al. 1998). Consequently some studies of potential pathogens
(listed under microbial and invertebrate pathogens below) are directed
at control of pathogens rather than control of shepherd's purse as a
weed.

**Microbial pathogens**. A number of fungal pathogens have been reported
to infest shepherd's purse, including *Alternaria brassicae*, *A.
brassicicola*, *Leptosphaeria maculans*, *Verticillium dahliae* (Cooke
et al. 1997, Henriksson 1995, Petrie et al. 1995). *Capsella* also is
know to be a host of beet yellowing viruses, which cause deleterious
effects to certain mustard crops (Stevens et al. 1994), and tomato
spotted leaf virus (Bitterlich and McDonald 1993).

**Insect pathogens**. Several invertebrates have been identified as
infesting shepherd's purse, including nematodes (*Meloidogyne hapla*),
and cotton aphids (*Aphis gossypii*) \[Belair and Benoit 1996, Hosoda et
al. 1993\].

**Herbicide control**. Several herbicides have been found to be
effective in controlling shepherd's purse, including imazethapyr
(Darwent et al. 1997), 2,4-D (Cudney et al. 1993), rimsulfuron (Eberlein
et al. 1994), dimethenamide (Quaghebeur 1993), and paraquat (Foy and
Witt 1993). Staats and Klett (1993) evaluated several pre-emergent
herbicides (Surflan, Pennant, Gallery, and Treflan) , in attempting to
control *Capsella* under greenhouse and container-grown conditions.
Lorenzi and Jeffery (1987) recommend dinoseb, paraquat, or soil
sterilants in fallow fields.

**Other control methods**. Fire, using propane generated flames, proved
unsuccessful in eliminating shepherd's purse relative to other weeds in
certain crop fields (Ascard 1995).

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