Prickly sida

Sida spinosa L.

Images above: Left: Prickly sida seedling (Antonio DiTommaso, Cornell University). Right: Prickly sida plant (Randall Prostak, University of Massachusetts).

Images above: Left: Prickly sida showing short flower stalks and the presence of leaf stems (Carroll Johnson). Right: Arrowleaf sida showing stemless leaves and long flower stalks (Carroll Johnson).

Identification

Other common names:  spiny sida, prickly mallow, false mallow, Indian mallow, thistle mallow, teaweed

Family:  mallow family, Malvaceae

Habit:  In the temperate zone, this species behaves as an upright summer annual; in tropical regions, it is a somewhat shrubby perennial (USDA Plants).

Description:  Seedlings have notched, round to heart-shaped, 0.3-0.6” (0.8-1.5 cm) long by 0.2-0.3” (0.5-0.9 cm) wide cotyledons.  The first pair of true leaves is round, subsequent leaves are ovate to triangular.  Long-stalked young leaves, are alternate with toothed edges.  The seedling stem, cotyledon edges, and leaf edges are covered in short hairs.  Mature plant stems are erect, highly branched, lightly hairy, and can reach 0.7-3.3 ft (0.2-1 m) in height.  Leaves are alternate, 0.8-2” (2-5 cm) long by 0.4-0.8” (1-2 cm) wide, lanceolate to oval, toothed, and have a 0.4-1.2” (1-3 cm) stalk; stipules are linear, and leaves may also have a 0.2-0.3” (0.5-0.8 cm) spine at the base.  Leaf surfaces and stalks are covered with short hairs.  The root system is a long, slender, branching taproot.  Flowers are produced individually or clustered from leaf axils, on 0.08-0.5” (0.2-1.3 cm) stalks.  Each flower has 5 pale yellow, 0.16-0.24” (0.4-0.6 cm) long petals.  Stamens are fused for most of their length, forming a column.  Seeds are located in five-chambered capsules that split into five sections when mature; each section has two sharp spines at its apex.  Seeds are 0.04-0.1” (0.1-0.3 cm) long, and reddish brown, with two flat and one rounded side.

Similar species:  Arrowleaf sida (Sida rhombifolia L.) leaf stalks are nearly absent, and much shorter than the flower stalks, whereas prickly side leaf stalks are longer than the flower stalks.  Virginia fanpetals [Sida hermaphrodita (L.) Rusby] is closely related to prickly sida, but can be distinguished by its white to pale pink flowers, lobed leaves, and taller height (up to 10 ft) at maturity.  Young prickly sida seedlings may resemble velvetleaf (Abutilon theophrasti Medik.) seedlings, but lack distinctive, velvety hairs.

Management

Prickly sida emerges in late spring and summer (Egley and Williams 1991) and grows best in hot conditions (Teem et al. 1974).  Consequently, it is a poor competitor and easy to control in winter grains and cool season vegetables.  Winter grains and early planted spring grains can be harvested before it goes to seed, thereby interrupting the life cycle.  Because the seeds die off relatively quickly in the soil, rotation into hay for a few years can greatly decrease an infestation.  Fall seedings of the hay can be timed to prevent reproduction during the establishment year.  A spring seeding will require at least two carefully timed mowings: the first to catch the young prickly sida in the 2-4 leaf stage and the second a few days after the weed begins to flower, and an additional mowing may be required to prevent reproduction by late emerging plants.

Prickly sida is most troublesome in summer row crops like cotton, soybeans, corn and sorghum.  Since prickly sida seeds die off relatively quickly and seeds must be close to the soil surface to successfully produce seedlings, populations will be easier to manage with annual moldboard plowing than with reduced tillage regimens.  This should occur either in the spring or fall, but not both, or some seeds will be plowed back up in the spring before they have had a chance to die off.  Delaying soybean planting until mid-June will get the crop past the primary peak in prickly sida emergence.  Tine weed as long as possible into the June emergence period.  Cultivate shallowly to avoid bringing up new seeds into the near surface emergence zone.  Flame weed cotton to destroy late emerging weeds in the crop row.  Although close spacing of row crops can reduce light penetration and the growth of prickly sida (Molin et al. 2004), the benefits will rarely compensate for the reduced opportunities for cultivation.  Prickly sida responds strongly to P fertility, so supply needed N with cover crops or plowed down sod and minimize manure and compost use.

Prickly sida is among the species most susceptible to solarization.  Covering soil with clear plastic for 1-3 weeks in mid-summer in Mississippi killed most seeds in the near-surface soil and reduced subsequent emergence by over 90% (Egley 1983).  The species also can be suppressed with straw mulch (Correla and Durigan 2004).  Prickly sida seeds are susceptible to destruction at heat levels generated by narrow-windrow burning of soybean reside (Norsworthy et al. 2020).

Ecology

Origin and distribution:  Prickly sida is native to the U.S.A.  It occurs widely in the Southeast and Midwest, and sporadically in the Southwest and Northeast (USDA Plants).  It is widely distributed in tropical and subtropical regions of both hemispheres (Baskin and Baskin 1984), including Mexico, South America, Hawaii, India, and Australia (Holm et al. 1979).

Seed weight:  2.3 mg (Mohler, unpublished data)

Dormancy and germination:  Most newly matured seeds of prickly sida are dormant due to a water impermeable seed coat.  Some newly matured seeds (15-32%), however, will germinate immediately at day/night temperatures of at least 86/59 °F (30/15 °C), with percentages increasing with temperature up to 104/77 °F (40/25 °C) (Baskin and Baskin 1984).  Normally, water only enters the seed following weakening of cells in the region where the seed attached to the parent plant (Egley and Paul 1981, 1993).  Damage to the seed coat (scarification) also allows the seeds to take up water and results in nearly 100% germination over a wide range of temperatures from 59/43 °F (15/6 °C) to 104/77 °F (40/25 °C).  Aging intact seeds for 16 weeks in either continuously moist or alternating wet-dry conditions substantially increases germination to as much as 78% when seeds are subsequently germinated in a warm temperature regimen 104/77 °F (40/25 °C) (Basking and Baskin 1984).  Similarly, storing the seeds dry at room temperature for 3-9 months results in germination of 42-95%, with percentage germination increasing with the incubation temperature (Egley 1976, Baskin and Baskin 1984).  In contrast, 12 weeks of freeze/thaw cycles or incubation at 41 °F (5 °C) did not promote germination (Baskin and Baskin 1984).  In two other studies, over 70% of seeds germinated at 95-104 °F (35-40 °C) after storage for 2-4 months or longer at 41 °F (5 °C) (Egley 1976, Smith et al. 1992).  When seeds were incubated in various temperature regimens from November to August, total germination over the period and the rate of germination increased with temperature up to 104/77 °F (40/25 °C). Germination was quickest when seeds were subjected to 30 day wet/dry cycles (Baskin and Baskin 1984).  Light does not promote germination (Egley 1976, Smith et al. 1992).  Seed germination is high at pH 5.0-8.0 (Smith et al. 1992).  In short, seeds become permeable and able to germinate after remaining in the soil for several months in either a wet or dry or alternating wet/dry state, and germination is most rapid and complete with warm temperature regimens.  Sustained temperatures of over 113 °F (45 °C) however, kill seeds (Smith 1992, Egley 1990).

Seed longevity:  Less than 1% of prickly sida seeds remained viable after 5.5 years of burial (Egley and Chandler 1983).  From 22 to 27% of prickly sida seeds remained viable after 1.5 years of burial giving an estimated annual mortality rate of 60% (Egley and Chandler 1978).  When a sowing of prickly sida was tilled annually to various depths, the number of seeds declined by an average of 88% per year over a two-year period (computed from Egley and Williams 1990).  Nevertheless, a few seedlings were still emerging after 5 years (Egley and Williams 1990).                                          

Season of emergence:  In Kentucky and Mississippi, prickly sida emerges from April through September (Baskin and Baskin 1984, Egley and Williams 1991).  Repeated counts through five seasons in Mississippi showed two peak periods of emergence, one in May and another in July-August (Egley and Williams 1991).

Emergence depth: Emergence is poor at the soil surface, best from 0.2” (0.5 cm) and declines rapidly with greater depths.  No seedlings emerge from deeper than 2” (5 cm) (Smith et. al 1992).

Photosynthetic pathway:  C3

Sensitivity to frost:  Prickly sida is sensitive to frost (Schummer et al. 2012).

Drought tolerance:   Prickly sida can maintain leaf function at higher water stress levels than other weeds and had the highest water-use efficiency compared to other C3 (but not C4) weeds (Patterson and Flint 1983).

Mycorrhizae:  Prickly sida is mycorrhizal (Tungate et al. 2007).

Response to fertility:  Prickly sida is most commonly found on soils with high P (Korres et al. 2016) and it grew 5-fold larger on soil testing high in P relative to soil testing very low.  It grew 40% better on soil testing high in K than on soil testing low or medium (Hoveland et al. 1976).   The species occurs most frequently on soils with a pH of 5.5-6.5 (Korres et al. 2017) and growth is substantially reduced at pH of 5.2 or lower (Teem et al. 1974, Buchanan et al. 1975).

Soil physical requirements:  The species is typically found on fertile loamy soil (Hilty 2017).  It occurs most frequently on soils with low compaction and good internal drainage (Korres et al. 2017), but it tolerates poor drainage (USDA Plants).

Response to shade:  Prickly sida prefers full or partial sun (Hilty 2017).  Growing cotton at a high density of 124,000 plants/acre (309,000/ha) in narrow 10” (25 cm) rows rather than a normal density of 40,000 plants/acre (100,000/ha) and wide 39” (100 cm) rows reduced light penetration through the cotton canopy by 71-81%.  In the narrow row cotton, prickly sida were no shorter, but were less branched and weighed about half as much (Molin et al. 2004).  In experiments with shade cloth, prickly sida was well-adapted to shade environments.  It produced higher growth and reproduction under mild shade (30-50%) than no shade, and showed suppression only at a high (90%) shade level (Copes 2016).

Sensitivity to disturbance:  One mowing close to the ground between sorghum rows was sufficient to kill most plants and provided between-row control similar to that of a broadcast herbicide program (Donald 2007). The species tolerates cattle grazing well (Fensham 1999).

Time from emergence to reproduction: In Illinois, plants flower from mid-summer to early fall (Hilty 2017).  In Mississippi, flowering occurs from June until frost (Schummer et al. 2012).  Seeds become viable 12 days after flowering, but continue to dry and develop a hard seed coat for another 9 days before becoming mature (Egley 1976).

Pollination:  Prickly sida is primarily self-pollinated, and many flowers pollinate without ever opening (Harms 1965).  The flowers attract bees and butterflies (Hilty 2017), and it also outcrosses to a small extent (Harms 1965).

Reproduction:  Each flower produces a fruit composed of five segments that contain one seed each (Uva et. al. 1997).  Prickly sida produced 1,900 seeds per plant in full sunlight, and 3,000 seeds per plant under the optimum 30% shade environment (Copes 2016).  However, it produced 8,100 seeds per plant when exposed to shade early followed by full sun later in the season, suggesting that it is especially adapted to reproduction during the crop senescence period (Copes 2016).  From 36 to 79% of seeds were shattered by the time of soybean harvest in Arkansas (Schwartz-Lazaro et al. 2021).

Dispersal:  Spines on segments of the seedpods can cling to fur or clothing and thereby distribute the seeds (Hilty 2017).  Capsule segments float (Mohler, personal observation), so the species probably also disperses by water.

Common natural enemies: Three-cornered alfalfa hopper (Spissistilus festinus) feeds on prickly sida (Moore and Mueller 1976).

Palatability:  Prickly sida has better digestibility than common southern forage grasses and has similar levels of crude protein, but is deficient in P.  Inclusion of some prickly sida in hay or silage still provides good animal nutrition (Bosworth et al.  1980).  Its palatability is relatively low, however, as indicated by its increasing abundance in response to the intensity of cattle grazing (Fensham et al. 1999).

References:

  • Baskin, J. M. and C. C. Baskin.  1984.  Environmental conditions required for germination of prickly sida (Sida spinosa).  Weed Science 32:786-791.
  • Bosworth, S. C., C. S. Hoveland, G. A. Buchanan, and W. B. Anthony.  1980.  Forage quality of selected warm-season weed species.  Agronomy Journal 72:1050-1054.
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  • Copes, J. T.  2016.  Prickly sida (Sida spinose L.): Biology and in-crop and post-harvest management programs.  LSU Dissertations 1279.  https://digitalcommons.lsu.edu/gradschool_dissertations/1279
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