Spartina densiflora is a cordgrass that grows caespitosely and has been known to form small meadows (Pfauth, 1998). Stems are up to 1.5 meters in length and are glabrous like the leaves which are inrolled when fresh, with pronounced ridges and leaf margins minutely ciliate. Rhizomes are present, though they are thin and wiry (Pfauth, 1998).

Spartina densiflora shows great phenotypic plasticity. It may vary between a tall form of 1.5 m and a short form of few centimeters tall (often called the Patagonian form). The density of inflorescences, spikes, spikelets, and their shape and size may vary importantly among plants (and that is why the common name “densflower” may lead to the misidentification of introduced clones) (Dr. Alejandro Bortolus, pers.comm., 2009).

Spartina densiflora demostrates a pattern of sequential development of identical growth units derived from tillers. Populations of S. densiflora are sustained by the growth of live shoots to support an annual die-back phase (Castillo, 2007). Spring to early fall is the time for rapid growth and development. S. densiflora blooms from April through July when it experiences the die-back phase with the loss of flowering culms (NWCB, 2007).
S. densiflora does not show a clear dormancy period during the year within its native range (Bortolus 2006).

Spartina densiflora provides shelter from predators and nest building material for birds in southern South America, birds include two rare and endemic species as well as nearly 35 other bird species that use the marsh for migration (Bortolus, 2006). Mammals also benefit from the growth of S. densiflora as a place to feed and breed in urban areas where other such places may be scarce (Bortolus, 2006). In native ranges S. densiflora provides mass quanitities of detritus to estuarine systems annually (NWCB, 2007).

Spartina densiflora is capable of invading a broad spectrum of habitats from intertidal marshes to terrestrial ecosystems. Soils that can support S. densiflora vary from well drained and oxygenated, to muddy and anoixc (Bortolus, 2006). Within the tidal marsh itself, S. densiflora outcompetes native flora between the lowest and highest topographic levels (Nieva, 2001). S. densiflora inhabits estuaries as well as open coastline where it succesfully populates rocky shores of softer limestone substrate or hard volcanic rock (Bortolus, 2006).

Spartina densiflora relys on both vegetative tiller production and seed germination to drive expansion over a range of salinities. The lack of a dormant period allows S. densiflora a competitive advantage over other species. Studies show that the germination rate of seeds are limited with increased salinities (Kittleson, 1997). In addition, higher desities of propagules can be found at higher elevations within the marsh. A negative correlation between rate of flowering and rate of propagule production exists (Nieva, 2001). Population density as well as competition effect these rates of establishment and reproduction as undisturbed areas are much more vulnerable to colonization success (Kittleson, 1997). Both sexual and asexual reproduction are a part of the reproduction of S. Densiflora, but the asexual role is very small in comparison (Nieva, 2001).

The photosynthesis process for S. densiflora can be impacted by the increase in salinity levels. Leaf expansion and leaf water potential are negatively correlated with salinty concentrations. The die-back on S.densiflora is significantly increased when a carbon inbalance is present. This is possible when the short photoperiods and anoxic sediments place more physiological stress on the plants than they can handle. This process causes a lower count of live shoots to be produced, thus making the die-back more catastrophic to the future survival of the plant (Castillo 2005).

Competition between Spartina densiflora and native flora leads to a loss of local plant biodiversity and decline of species specific habitats, which negatively effects local fauna. The increased invasion of S. densiflora can lead to a rise in marsh elevation because of plant presence on mud flats, thus limiting water flow and increasing sedimentation (San Fransisco Estuary Invasive Spartina Project, undated).
S. densiflora adds more complexity to mudflat habitats and it may increase local abundance and diversity of the associated fauna (Dr. Alejandro Bortolus, pers.comm., 2009).

Physical: Manual or mechanical extraction as well as mowing, burning or covering are all management techniques that can work effectively on small populations of Spartina densiflora but have complications in areas with a large population.

Chemical: A combination of the aquatic herbicides imazapyr or glyphosate and surfactant is applied through various means directly to S. densiflora to eradicate and control populations of the invasive cordgrass. These two herbicides are currently the only aquatic chemicals approved for use in estuarine environments in the state of California by the USEPA and the California Department of Pesticide Regulation (CDPR) see (San Fransisco Estuary Invasive Spartina Project, undated).