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Broadleaf Weed Identification ToolKit

Plant morphology


Below is a schematic line drawing of a broadleaf plant. Notice the alternate leaves on top, while the second (middle) set of leaves are opposite one another.

1050t.JPG (4833 bytes)

This is another schematic line drawing. The top set of leaves are both lobed (left) and ovate (right) as well as alternate to each other. The second set of leaves are opposite and are the seed leaves: cotyledons.

1126t.JPG (4336 bytes)

Keep in mind no real plant species would have this combination of leaf to stem arrangement, either it will be alternate or opposite or some other single arrangement.


LEAVES

Leaf Shape

Leaves come in many shapes, here are a few:

heart-shaped 1053t.JPG (4796 bytes) lobe-shaped 1057t.JPG (5462 bytes)
spade-shaped 1058t.JPG (6489 bytes) arrow-shaped 1059t.JPG (4769 bytes)
star-shaped 1060t.JPG (7141 bytes) pentagon-shaped 1061t.JPG (7247 bytes)
oval 1071t.JPG (6424 bytes) ovate 1072t.JPG (6027 bytes)
elliptical 1073t.JPG (5723 bytes) lanceolate 1074t.JPG (5682 bytes)
oblong 1075t.JPG (6636 bytes) spoon-shaped 1076t.JPG (6550 bytes)


Cotyledon leaf shape

Cotyledons are the seed leaves. As a broadleaf weed species seed germinates, the seed leaves expand and start giving farmers problems. This is the hardest time in the life cycle (except maybe fishing seeds out of the soil seed bank) to ID a weed. Here are some generic cotyledon leaf shapes:

linear 1111t.JPG (4763 bytes) oblong 1112t.JPG (3997 bytes) lanceolate 1113t.JPG (4602 bytes)
ovate 1114t.JPG (4366 bytes) spatulate 1115t.JPG (4076 bytes) oval 1116t.JPG (4456 bytes)
round 1117t.JPG (4212 bytes) kidney 1118t.JPG (5640 bytes) butterfly 1119t.JPG (9031 bytes)


Leaf margins


Leaf margin morphology can be helpful in ID.

Left: entire; left center: serrate; right center: dentate; right: crenate
1019a.JPG (5715 bytes)

Left: sinuate; left center: sinuate & distantly toothed; right center: toothed; right: lobed
1019b.JPG (5096 bytes)

The parallelism of leaves can be helpful, especially with the bindweeds:

parallel leaf margins 1062t.JPG (4579 bytes) non-parallel leaf margins 1063t.JPG (4256 bytes)


Leaf venation

Sometimes the veins in the leaf can help in weed ID. They are usually rounded and protrude above the leaf surface.

palmate venation 1122t.JPG (8960 bytes) 3 prominent veins 1179t.JPG (4719 bytes)
pinnate venation 1123t.JPG (5497 bytes) or 1125t.JPG (6385 bytes)


STEMS

Several interesting and cool features about stems and branches can help you ID broadleaf weeds. The first is the arrangement of branches relative to the main axis. The branches can be opposite (below, lower set of leaves) one another or they can alternate (below, top set of leaves):

1120t.JPG (6741 bytes)

alternate 1052t.JPG (4582 bytes)
opposite 1086t.JPG (4945 bytes) 1121t.JPG (7121 bytes)

Ochrea
Plants in the Smartweed, Polygoneaceae, family have a distinctive membranous sheath that surrounds the branch-main axis junction, the ochrea (below).

1051t.JPG (5599 bytes) 1186t.JPG (6086 bytes)


Below are two examples of the ochrea: Pennsylvania smartweed (left, no hairs on ochrea) and ladysthumb (right, hairs on ochrea).
Pennsylvania smartweed: 526t.JPG (6523 bytes) ladysthumb: 515t.JPG (10155 bytes)


Root systems
The root system of a weed can be very helpful in ID. Below are some examples:

fibrous root system 1016ft.JPG (7707 bytes) 1109t.JPG (5415 bytes)
taproot 1016Tt.JPG (7245 bytes) dandelion taproot 218t.JPG (14393 bytes)
rhizome 1108t.JPG (5190 bytes)



©jdekker-2003

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