Introduction to Grasses

i Aug 3, 2010 No Comments by

Wake Audubon Board members are the bloggers for the next few months.  This week’s blogger is long time board member Erik Thomas.

Introduction to Woodland Grasses

By Erik Thomas

This is the time of year when bird songs are being replaced by insect calls—cicaidas, katydids, and the like.  It’s also the time of year when the woodland wildflowers, or at least most of them, have died down until next spring, to be replaced by—well, by what?  Woodland grasses are one of the main plant groups that appears during the heat of summer.

Most people think of grasses as plants that grow in full sun.  However, we have several common woodland grasses in the Triangle area.  Most of them would make good ornamentals if you have shady spots and you need some greenery there.  These aren’t the kinds of grasses that you can mow, however.  They should be treated like ornamental flowering plants.

A couple of our common woodland grasses appear in the spring and then go dormant.  These species are Twoflower Melicgrass (Melica mutica) and Fowl Mannagrass (Glyceria striata).  They don’t look much alike.  Twoflower Melicgrass grows a foot tall or less and the stems have a series of seedheads that hang down from them.  Each seedhead has only two seeds in it and together they look like a big wheat grain.  It grows in well-drained sites.  Fowl Mannagrass, on the other hand, is tall and likes to have its feet wet.  It grows four or five feet high and you’ll find it in sites that have a little standing water after a heavy rain.  Its stems have lots of branches, and at the end of each branch is a small seedhead with several tiny seeds.

Giant Cane (Arundinaria gigantea) is in a group by itself.  It and its shorter down-east relative, Switch Cane (Arundinaria tecta), are our only native bamboos, but they don’t look like stereotypical bamboos.  Around here, Giant Cane usually grows three to six feet tall, though it can get much taller, and the stems look like reeds with leaves coming off them at intervals. The stems each live for more than one year.  It forms thickets in bottomland woodlands, normally where the soil is wet but not flooded.  These thickets are known as “canebrakes” and were a lot more extensive before Europeans came to America.  One bird species, the Swainson’s Warbler, is associated with canebrakes, and it’s thought that Swainson’s Warblers were a good deal more numerous back when the South had vast canebrakes.

A common species that appears in midsummer is Woodreed (Cinna arundinacea).  You see it as individual stalks growing in moist, shady woodlands.  The leafy stalks are about three feet tall.  They usually have several kinks near the base and then a long straight section leading to the seedheads.  The seedheads themselves grow on short branches at the top of the stalk.  All the seedheads together give the plant a soft, plume-like appearance.

Two late-summer species that are easy to grow are River-oats (Chasmanthium latifolium) and its cousin, Slender Wood-oats (Chasmanthium laxum).  Actually, I’m assuming that Slender Wood-oats is easy to grow.  I’ve grown River-oats and it’s really easy to cultivate, so I figure that Slender Wood-oats ought to be easy, too.  I’m hoping to find out for sure within the next year, assuming that I remember to collect some seeds this fall.  Both of these species grow in bottomlands that are partially shaded.  Their seedheads are flattened.  In fact, these flattened seedheads fooled botanists a century and more ago into thinking that they were closely related to Sea-oats (Uniola paniculata), which also has flattened seedheads, and they put River-oats and Slender Wood-oats in the genus Uniola.  Later on, the botanists figured out that the similarity was only superficial and gave them their own genus, Chasmanthium.  River-oats and Slender Wood-oats both grow about two feet tall and can form dense colonies.  In River-oats, the seedheads are diamond-shaped overall, about half an inch long and a third of an inch wide, and quite attractive.  They turn golden-brown or purplish-brown when they ripen in the fall and stay on the stems until winter.  In Slender Wood-oats, the seedheads are chevron-shaped.  River-oats is sometimes available in nurseries.  It tends to spread out over time by seeding and some people find it too aggressive for a garden, but it can be effective at stopping erosion in woodland gullies.

Some grasses have long awns in their seedheads, just like bearded wheat.  Awns are needle-like structures that grow underneath each seed and may be an inch long.  Three common woodland grasses have awns like that.  Bottlebrush Grass (Elymus hystrix, listed in many manuals as Hystrix patula) likes drier situations and is more common west of Durham than to the east.  It’s easy to recognize because the seedheads at the top of each stem look like a bottlebrush.  The seeds and awns stick straight out from the stem in four rows.  If you look down the stem from the end, the seeds make an X.  Another species with long awns is Bearded Shorthusk (Brachyelytrum erectum).  Its seeds and awns don’t stick out from the stem—instead, they press against the stem, making the seedheads look a lot more like an ear of bearded wheat.  Unlike wheat, the seeds don’t grow in two rows, they’re smaller than wheat grains, and there aren’t anywhere near as many seeds in one head.  Bearded Shorthusk likes the shade.  It forms loose clumps in dry to moderately moist forests.  The third common awned species is Common Wild-rye (Elymus virginicus).  Common Wild-rye likes moist sites on the edges of woodlands.  Its heads look a lot like the head of a cereal grain.  They have lots of seeds in them.  However, the seedheads are round, not flattened, because the seeds don’t grow in two well-defined rows.  Its awns are only about half an inch long or less.  All three of these species grow in the summer.

One late-summer woodland grass that you don’t want to grow is Japanese Stiltgrass (Microstegium vimineum), also called Nepalese Browntop.  This species is native to Asia and was accidentally introduced because shippers in Asia years ago had used it as cheap packing material for packages they sent here to the United States.  Once the packages got here, people threw out the dried grass, which came complete with seeds, and the seeds sprouted.  Japanese Stiltgrass has been taking the South by storm.  You’ll find it growing in any wooded park or greenway in the Triangle.  You may have it in your yard, too.  This time of year, it looks like pleasant greenery carpeting forest floors.  Once its seeds get ripe in October, it rapidly turns brown and dies off.  It’s extremely aggressive and crowds out other plants.  The only good thing I can think of about it is that it’s easy to pull up.  Whereas the other grasses I discussed above are perennials and have strong root systems, Japanese Stiltgrass has a weak root system because it’s an annual.  If you try to get rid of it, you’ll need some persistence.  The seeds can remain viable in the soil for several years, so even if you kill one year’s crop, old seeds will sprout the next spring.  Don’t hesitate to fight the good fight, though.  Japanese Stiltgrass can be recognized because its leaves are rather short for a grass, only one to three inches long and about a quarter to half an inch wide.  While other grasses have leaves shaped like swords, Japanese Stiltgrass has leaves shaped like daggers.  The stems lop down on the ground or, in dense colonies, arch upward, and they grow in a zigzag fashion.