Authors: Jeffrey Firestone, Global Invasive Species Team, The Nature Conservancy
- Ripidium ravennae is a tall clumping grass with a basal tuft of leaves and flowering stalks that reach heights of 8-12 ft. (2.4-3.7 m), towering over big bluestem and other plants and making them easily visible from a distance. The base of the clump can be several feet in diameter indicating a sizeable root mass.
- The basal tuft of leaves and stems are covered with fine hairs.
- Flowers are feathery, fan-shaped, terminal panicles. They are silvery to pink in color and up to 2 ft. (0.6 m) long. Flowering occurs September through October.
- Purplish spikelets are 0.12-0.24 in. (3-6 mm) long. They are spread by wind.
- Ecological Threat
- Ripidium ravennae has been observed spreading from plantings along roadsides and other disturbed edge habitats as well as in fields and other open sites. Control is difficult with the most effective method simply to physically remove the plants by pulling or digging them out. Ripidium ravennae is native to southern Europe and was introduced for ornamental purposes.
- Plant Invaders of the Mid-Atlantic Natural Areas
- Flora of China, www.eFloras.org
- USDA NRCS PLANTS
- USDA ARS GRIN
Saccharum ravennae (L.) L.
Erianthus ravennae (L.) Beauv.
Ravenna grass, ravennagrass, Hardy Pampas Grass, Hardy Pampasgrass; Plume grass
A tall, dramatic bunchgrass that has escaped from horticulture into wetlands and river channels. Ravenna grass will grow as separate plants in excess of six feet tall. It has long blades that extend up and arcing from the center, with bamboo-like flowering canes emerging from the center. The canes do have some nodes, although they are annual and generally are roughly a centimeter in diameter. The canes raise large flowering plumes above 10 feet. The plumes look rather like feather-dusters, and can disperse tiny seeds with feathery attachments on the wind.
There are no US natives that it is known to resemble, due to its dramatic size, but not all the grass flora is known to this author. It most strongly resembles the horticultural and invasive Pampas grass and Jubata grass (Cortaderia selloana and Cortaderia jubata). Also large bunchgrasses with plumes, Ravenna grass can be distinguished by three main factors: the other two species have sharply serrated leaves that can cut a hand but no hairs, while Ravenna has weakly serrated leaves with hairy bases (curled around the other leaves, below the blade joint); Ravenna grass has plumes even taller than pampas, borne on stalks that stand well above the leaves and have nodes or joints, while the Cortaderia spp. have plumes on node-free stems that appear to be built similarly to the leaves; Ravenna grass is much more cold-tolerant than pampas grass, and somewhat more cold-tolerant than jubata grass, so states with regular freezes are much more likely to see Ravenna (See Natural History section for reported ranges). Ravenna grass also tends to have a thick white vein on the center underside of a leaf.
The blade part of the leaves seem to be longer than most prairie grasses, even the biggest like switchgrass, and the seed stalks are distinctive. Phragmites australis and Arundo donax do have plumes borne on stalks, but the leaves are much shorter and strap-like, and borne off the stalks rather than separately from the base.
Ravenna grass is a new addition to the invasive plant catalog, although it has appeared in horticultural trade as a minor player since at least 1921. It primarily establishes on the margins of riparian zones, although growth on gravel bars in mid-channel is also common. It can increase to monoculture under these conditions. As a newly recognized problem, and with comparatively few invasions recorded, many of the impacts are partly speculative based upon similarity to Cortaderia jubata, Cortaderia selloanaselloana and other invaders of the same habitat type. At this point, it may be prudent to discourage use and persistence of this plant so that we are not able to fully document how bad its impacts could be.
Ravenna grass can establish with relatively little disturbance, and natural disturbance is more than ample (e.g. natural seep on inaccessible cliffs, natural stream bank erosion). It can form impenetrable stands of one species, and can grow out from under other vegetation. It will exclude native communities through competition, although not consistently. It appears to specialize in moist areas, including in California, Utah, Grand Canyon and Arizona, and so it may be more effective at harming important or rare species than its area/extent suggest, given the infrequency if moist habitats in those states.
It produces copious biomass in areas that generally have relatively little, especially by growing on harsh substrate like gravel banks, and being much taller than surrounding vegetation. This would change the shade profile, plant competition and flammability of the community. Older stands may be able to carry fire that would not normally work in riparian vegetation. It can anchor soils normally more subject to shifting (e.g. mid-channel) and act as a physical barrier to stream flow through its biomass and accumulation of flotsam, thatch and sediment. This may shift erosion locations.
Experience in San Diego area estuaries suggests that Cortaderia selloana uses much more water than the vegetation in replaced. Although the cooler climate may make this less likely, the high large increase in leaf area over some of the native communities it replaces may also facilitate water usage.
Ravenna grass is native to the Mediterranean, and is names for the town of Ravenna, Italy.
It has been reported to be growing well away from human cultivation in Cache Creek, northern California, rivers in Oklahoma and Arizona, wetlands in Michigan and near Roswell, New Mexico and in seeps and other rare moist communities in CA and UT. It appears to require moisture for naturalization, as its habitat generally is wetland edge, flood plain above the high-water mark, and other places with moisture and a micro-site of bare soil, sand or rock. It can frequently be found in suburban yards across much of the US.
It is dispersed througout the US as an ornamental grass, and has been sold, consistently but infrequently, for 90 years. It is currently recommended for planting by several state extension services and botanic gardens. The invasion in the Grand Canyon resulted from deliberate planting as it considered at the time to be a recommended, safe plant.
It is a perennial bunchgrass that is hardy from zones 5a (some report 4b) to >9. Based upon existing reports from NM, AZ, and southern CA, the upper limit of zones and warmth is probably indefinite as long as moisture is available. It grows quickly. It will die back during a freeze, leaving copious amounts of dry leaves and standing stalks, and regrow vigorously. It flowers in late summer, although this may be habitat dependent. Individual flowers are small and, like many grasses, inconspicuous, but the plumes for which this grass is ornamentally valued contain hundreds or thousands each. It reproduces through copious production of seed. It is not known how many years until seed production begins. Seeds are small and disperse readily on the wind, esp. with a 10 foot height advantage. They probably float on the surface tension of the water as well. As the seeds are small, a seed bank is less likely, but this is not known.
No methods are specifically indicated for this species, as it is a new problem. Control can be expected to be similar to recommendations for the species provided here, from morphology. Ravenna grass is a distant relative of sugar cane, and some research may be available for this species on herbicide tolerance; there are also two peer-reviewed articles on herbicide tolerance for control of weeds around desirable horticultural ravenna grass that may be available for guidance.
Physical control: Probably effective, esp. for small clumps before reproductive size. However, there is a good chance that merely mowing / grazing would be inadequate because this plant is said to resprout after damage. Removing the roots and ensuring that they are either removed, or prevented from contacting moist soil is recommended. If leaving on-site, the plants should be placed off moist soil so that they can dry and die without rerooting. Containing the seeds so that they do not disperse during control efforts will reduce reinfestation the following season. Beware of the hairs on stalks and leaf bases. Although not especially irritating, they can be somewhat unpleasant. The Grand Canyon has experience using physical control for several years.
Burning is not expected to be sufficient, as they may resprout from the moist and insulated roots, although this has not been examined.
Chemical Control: Several post emergent herbicides should be effective. Glyphosate in the fall is likely the most chemically effective, but spraying before seed production is also desirable to prevent reseeding. Glyphosate could provide either area control or targeted elimination while preserving neighboring plants, due to its ability to translocate. Currently, the Yolo County Resource Control District, and UC Davis are experimenting with various types of chemical control.
Arizona Weeds and Invasive Plants Working Group (AZ-WIPWG) listed as "Medium-Alert" California Invasive Plant Council (Cal-IPC) listed as "Medium Red-Alert"
Spanish Working Group on Urban and Alien Plants (Dana et al n.d.) Rank 2/3, "it is known as invasive and although it is not threatening natural or man-made ecosystems, it is suspected to do it in the near future"
Branhagen (n.d.) for Kansas City rated as: Plants that are severe pests near where planted but whose seeds do not disperse great distances. These plants should not be planted near natural lands. However, he describes the S. ravennae as "A plant to watch…"
PhD Thesis, Lacy Jo Burgess, University of Oklahoma, Norman.
AZ-WIPWG review (broken link) by Dr. Ed Northam
Images from Bugwood.org