THIS WEEK at HILTON POND
15-30 June 2006

Installment #320---
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SEDGES HAVE EDGES . . .

When leading Guided Field Trips down the trails at Hilton Pond Center, we often come across clumps of green plants with narrow, grass-like leaves. Invariably, when we ask folks what the plants are, they respond with "some kind of grass." Often they're right--but sometimes they're not--at which point we ask them to grasp a stem of the plant 'twixt thumb and forefinger and describe its shape. If the stems AND leaves are all flat--as they are in the cluster of foliage illustrated in the photo just below--they likely would be correct in calling the plant a grass, but if the stem feels round or triangular it's something altogether different, at which point we'd be inclined to sing out this mnemonic little ditty:

Sedges have edges,
Rushes are round,
Grasses are hollow,
What have YOU found?

All text & photos © Hilton Pond Center

Grasses, sedges, and rushes are all vascular plants--they have specialized tissues that conduct water and minerals (via xylem) and food (via phloem) and also produce flowers and fruit--but within the plant world they are relatively primitive and are classified as monocotyledons. (Monocots have only one embryonic leaf in each seed, while the "higher" dicots such as acorns and beans have two.) Only a few grasses, sedges, or rushes develop woody tissue or reach heights of more than a few feet, and many are ground-hugging annuals that survive in a given locale only because of their prolific seed production. Nonetheless, these three kinds of plants are pervasive worldwide; one manual of flora lists 89 genera and 325 species in the Grass Family (Poaceae) and 16 genera and more than 280 species of sedges (Cyperaceae) and rushes (Juncaceae)--and that's just in North and South Carolina! Some grasses are very important agricultural crops, including wheat, hay, and barley in the U.S. (plus bamboo and rice in the Orient), while sedges such as Carex spp. and rushes (e.g., Scirpus and Juncus spp.) have relatively little economic value--except that sometimes they are so successful they out-compete more desirable flora in farm and garden. Note that people do eat parts of a few sedges (e.g., the corm of the water chestnut), and one sedge in particular--the 15-foot-tall species used to make papyrus--is of great historical significance. More important, he vast majority of grasses, sedges, and rushes are vital for wildlife as food and/or shelter--especially since rushes and sedges may still grow at the perimeter of aquatic habitats where humans often eliminate shrubs and trees.

One thing grasses, sedges, and rushes have in common is their flowers are relatively inconspicuous--even though blossoms on grasses are productive enough to yield clouds of pollen that causes hay fever in human sufferers. In general, flowers of all these plants are tiny and yellow-green, rust, or tan in color (see rush flowers above), so most folks--even experienced naturalists and botanists--often can identify only a handful of grasses, sedges, and rushes from memory by looking at floristic parts.

Fruits of the three plant groups in question are a bit more distinctive than their flowers, with some sedges producing inch-long prickly clusters of beak-like fruits (above); by comparison, many rushes make tiny globular fruiting structures (below) less than one-eighth-inch in diameter. Fruits of grasses are more variable, from plump kernels on an ear of sweet corn to the tiny, expensive seeds many folks scatter to create lawns that eventually get overtaken by free seeds from invasive grass species such as Crabgrass.

So if grasses and sedges and rushes look so much alike at first glance, what's a body to do when trying to differentiate them? Once again it's time to call upon that little poem we mentioned at the beginning of our photo essay:

Sedges have edges,
Rushes are round,
Grasses are hollow,
What have YOU found?

Indeed, a simple "touch test" is the giveaway for sedges, whose stems when rotated have a very noticeable triangular shape--hence a total of three "edges." To illustrate this characteristic, we clipped a flowering stem from a sedge and brought it back to the lab at Hilton Pond Center, where we made a fresh cut with a razor blade and placed the stem in front of our 3:1 macro lens. This allowed us to make the photomacrograph below that readily shows not only the triangular stem but also the sedge's vascular conductive tissue. (Keep in mind this is a highly magnified view; the stem is only about one-sixteeth-inch on each flat side!)

For the sake of comparison, we followed the same procedure on a rush stem and a stalk of grass. In our two other photomacrographs, the cylindrical ("round") nature of the rush's one-sixteenth-inch diameter stem is obvious (below) . . .

. . . while the grass (below) has a somewhat flattened stem that is noticeably "hollow." In both the rush and the grass vascular tissues are again visible.

We don't recommend clipping wild specimens just to learn whether they might be grasses, sedges, or rushes--after all, cutting kills the amputated part--but we do advocate a harmless "touch test" in the field to discover whether the plant is a sedge with triangular stems or a rush with round ones. Grasses--which typically have flattened stems and leaves--will be revealed by process of elimination, although it's important to remember to feel the sedge's triangular STEM rather than its flat LEAF. It should also be noted that a few genera of rushes (especially Juncus and Luzula spp.) may have flattened stems.

If in doubt about grasses, sedges, and rushes next time you're exploring a natural area like the habitats around Hilton Pond, just reach down and touch those mysterious grass-like plants, being careful to avoid Poison Ivy and all the while chanting our charming and unforgettable chorus:

Sedges have edges,
Rushes are round,
Grasses are hollow,
What have YOU found?

All text & photos © Hilton Pond Center
Thanks to Donna Wright of North Carolina State University for input


POSTSCRIPT: After posting this week's installment we heard from several folks who had different lyrics to the sedge-rush-grass rhyme. In particular, Kathy Miner of the University of Wisconsin-Madison Arboretum said her botany instructor taught it as:

Sedges have edges, rushes are round,
Grasses have nodes all the way to the ground.

Nodes are the conspicuous raised places on a grass stem that give rise to the leaves; the structures are much less obvious in sedges and rushes. Kathy also had heard:

Sedges have edges, rushes are round,
Grasses wear robes all the way to the ground.

This iteration refers to the way leaves of grass wrap around (clothe) the stem--as illustrated in our cross-section photo just above.


Comments or questions about this week's installment?
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Be sure to scroll down for an account of all
birds banded or recaptured during the period,
plus other nature notes of interest.



Thanks to the following fine folks for recent gifts in support of Hilton Pond Center for Piedmont Natural History and/or Operation RubyThroat: The Hummingbird Project. Your contributions allow us to continue writing, photographing, and sharing "This Week at Hilton Pond." (See Support if you'd like to make a gift of your own.)

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"This Week at Hilton Pond" is written & photographed
by Bill Hilton Jr., executive director of
Hilton Pond Center for Piedmont Natural History.

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BIRDS BANDED THIS WEEK at
HILTON POND CENTER

15-30 June 2006

SPECIES BANDED THIS WEEK:
Ruby-throated Hummingbird--1
American Goldfinch--1
Song Sparrow--1
House Finch--18

* = New species for 2006


WEEKLY BANDING TOTAL
4 species
21 individuals


YEARLY BANDING TOTAL (2006)
21 species
935 individuals


BANDING GRAND TOTAL
(since 28 June 1982)
124 species
47,517 individuals


NOTABLE RECAPTURES THIS WEEK
(with original banding date, sex, and current age)
NONE THIS WEEK

All text & photos © Hilton Pond Center


This Week at Hilton Pond
is part of the

OTHER SIGHTINGS OF INTEREST
--Because of intermittent travel away from Hilton Pond Center, this "week's" banding totals actually cover a fortnight. As expected, the Ruby-throated Hummingbird incubating a nest at Mountain Lake VA back on 20 May was no longer present during a re-check visit on 23 Jun. However, several more hummers were feeding from the sapsucker well--as was a juvenile Yellow-bellied Sapsucker.

--Since Song Sparrows (SOSPs) are a common bird, it might not seem unusual to see one in South Carolina in summer, but the one we trapped this week was only the second we've ever banded in June at the Center. Our part of York County seems to be devoid of breeding SOSPs, even though they nest throughout the northwestern corner of the Palmetto State. The species is not uncommon locally mid-October through mid-April, a period in which we've banded 344 since 1982, but only nine have been captured from May through September in 25 years. See Silent Spring Songster for a longer discussion of SOSPs in the South Carolina Piedmont.

--As always at the mid-year mark, we've updated our banding totals graphics at the Center since 1982. See Charts & Tables of Banding Results.


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