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Ornamental Grasses for Minnesota

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Common Name
Northern Sea Oats (Inland Sea Oats, Indian Woodoats. Broadleaf Chasmanthium)

 

Scientific Name
Chasmanthium latifolium (Michx.) H.O.Yates

 

Plant Family
Grass (Poaceae)

Garden Location
Not in the Garden

 

Prime Season
Early Summer

 

Grass structure and definitions - PDF from Oregon State University

Ligule Types, Shapes & Margins (pdf)

 

Northern Sea Oats is a clump forming warm season perennial grass on sturdy round stems from 2 to 4 feet in height. Stems are leafy and seldom branched.

Leaf blades are up to 7 inches long and up to 7/8 inch wide (22mm), broadest for most of the length until it tapers to the pointed tip, giving one of the alternate names of 'Broadleaf Chasmanthium'. Leaf sheaths and collars are smooth, usually free of hair but there can be a few long whitish hair. The lower part of the blade as it forms the sheath is usually brown. The ligule is small, less than 1 mm, and entire. The central leaf vein is prominent on the underside of the blade.

The inflorescence is an open panicle with branches nodding or drooping, green initially, turning brown at maturity. The axils of the panicle branches are sparsely hairy. The spikelets are up to 1-1/2 inches long and over 1/2 inch wide, with typically 6 to 17 florets, the lower 1 to 3 are sterile, the remaining fertile florets are positioned 45 degrees off the spikelet branch. The lower and upper glumes are veined as are the lemmas. Fertile florets have 1 stamen and 2 styles. Some plants may fertilize flowers without opening for external pollination - known as cleistogamous.

The seed is rarely exposed when mature - which is unusual in this genus as the genus name implies exposed seeds. The maturing spikelets have a very nice reddish-bronze color.

 

Habitat: Northern Sea Oats grows in full to partial sun in rich woodland soils, and along streams and river banks. As an ornamental it should have partial sun at a minimum, well drained soils, and adequate moisture. Dry sites should be avoided. The broad spikelets on drooping panicles provide good texture for landscape uses. It grows from a rhizomatous root system which can form colonies but the plant is a very slow spreader in northern climates.

Names: The genus name, Chasmanthium, is derived from two Greek words, chasme, meaning 'yawn' and anthos, meaning 'flower', together referring to the glumes of this genus which open like a mouth to expose the grain at maturity (except in this particular species). The species name, latifolium, means 'wide leaved'. The author names for the plant classification are: ‘Michx.’ refers to Andre Michaux (1746-1802), French botanist who made many exploring expeditions in the U.S. collecting and cataloging many species. His work was updated by ‘H.O.Yates’ which refers to Harris Oliver Yates (1934-2013), American botanist, teacher and Distinguished Professor of Biology at David Lipscomb College. His botanical work concerned seed plants and his work on the Chasmanthium genus is noted. An older scientific name for this grass is Uniola latifolia Michx. when it was classed in the that genus but Chasmanthium is now recognized as a distinct genus.

Comparisons: There are four other species of Chasmanthium, the main visual difference is that their panicle branches are erect to ascending. A variegated leaf cultivar of C. latifolia available from the nursery trade is called "River Mist". It tolerates more shade.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

plant drawing

Above: A good size clump in early August with spikelets maturing.

Below: The sheath and collar area usually does not have much if any hair. The spikelets have the florets placed at a 45 degree angle. The central vein of the leaf blade forms a ridge on the underside of the blade.

Stem green spikelets leaf blade underside

Below: The blades are wide for most of their length, then tapering to a point. The second photo is the leaf of the River Mist cultivar.

leaf blade River Mist leaf blade

Below: Maturing spikelets take on a nice reddish-bronze color. Second photo is of the River Mist cultivar.

mature spikelet Rivermist plant
mature spikelets

Notes:

Northern Sea Oats is native to a large section of the U.S., primarily the SE section, with a northern boundary of New Jersey and Pennsylvania, then west to Michigan, Wisconsin and Iowa, down to Kansas, New Mexico and Arizona and every state south of that line. It is not native to Minnesota but grows well in central and south Minnesota.

 

The other species of Chasmanthium are: C. nitidum, Shiny Woodoats; C. ornithorhynchum, Birdbill Woodoats; C. sessiliflorum, Longleaf Woodoats; and C. laxum, Slender Woodoats.

References and site links

References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.

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