Lab 1

Proper plant identification is an essential part of developing a proper weed control program. Control methods will vary according to plant species due to growth habits, life cycles, morphological characteristics, etc. The purpose of this exercise is to familiarize the student with some common weeds of New Mexico and to be able to identify these common crop, turf, and pasture weeds by sight. In this assignment you are required to collect and properly identify 30 common weeds. Five of the species must be grasses. You may turn in up to 20 additional specimens for extra credit. Of the 30 required weeds, 10 of them must be properly mounted on herbarium paper. Instructions for collecting, pressing, mounting, and labeling will follow later in the instructions. The department reserves the privilege of keeping any specimens as desired by the instructor. The weed collection will be graded according to correct identification, appearance of the plant, and labeling information. All students are required to turn in a weed collection to pass this course.

Collecting Plant Specimens

Selecting the specimens to be collected must be done with care. In most instances, collection of the entire plant makes the best specimen. Thus, identification references to stems, roots, leaves, flowers, or fruits, may all be made in taxonomic keys. However, with large weed specimens this is sometimes difficult to do. In such instances, the flower, a portion of the stem with a leaf, and roots may be collected. The plants should be average in size and free of various types of environmental damage (insect, drought, etc.). Choose your plant preferably from within a stand of many specimens of the same species. Woody plants will not be acceptable for turning in as part of the collection. Be selective! Do not get a whole mess of material but select two or three ideal plants for pressing and drying. Then, when they are correctly prepared, select the best one for mounting. All plants must contain reproductive parts (fruit, flower, seed, etc.). Make notes at the time of collection (see "Mounting") since ecological information will be needed for each specimen label. One way to collect this information is to assign a reference number to each plant as it is collected. Then, in a notebook this reference number can be written down along with the site information.

The following are some helpful collection tips:

• Collection should be started early in order to avoid difficulties in obtaining necessary specimens. This also allows time for proper drying and mounting of material.
• Collection bag: Students may use magazines or a plastic bag to hold samples while collecting in the field. The plastic bag will prevent plant wilting for nearly a full day.
• Collect more samples than you might need. After pressing, discard all but the best samples. Some specimens won’t press well.
• Collect enough of a particular plant for identification: flower or fruits, root system, and leaves.

Mounting

Plants will be mounted on herbarium paper which can be bought at the bookstore. Plants are to be mounted carefully, and only the best specimens should be mounted. Only one species should be put on each mounting page, place upright along the long axis of the page. The plant can be attached to the page either with small spots of glue (such as diluted Elmer’s glue) along the stem and leaves, or with small pieces of clear tape. Seeds may be taped down with clear tape. Each specimen must be accompanied with the following information on a 3x5 note card: common name, Latin name (family, genus, species), date of collection, place of collection (nearest town, county and state), habitat (including such things as slope, land use and other ecological data), and finally the name of the collector and any remarks. The note card should be placed in the folded newspaper with the plant. Mount enough of a plant for identification. Just a single leaf or flower is not enough. Include flower (or fruit), stem, leaves and roots in your mounted plant specimen.

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Label

Latin name: Family, Genus, Species

Date of collection

Place of collection: nearest town, county and state

Habitat (including such things as slope, land use and other ecological data)

Collectors name and any remarks

Identification

If possible, it is best to identify the plant at the time of collecting. At this time flowers and other plant parts can be looked at without damaging them. Later identification will be more difficult as parts will be brittle and difficult to handle for identifying. Some identification will be discussed in class, including several references to identification publications that are available for the students'’ use (see Course Outline).

Grading

The first 30 specimens will count towards 100 points of your laboratory grade. Each specimen is worth 3.33 points; 2 points credit will be given for correct identification and 1.33 points for specimen quality and the label. Each extra credit plant (31-50) is worth 0.5 points; therefore, it is possible to earn a maximum of 110 points for Weed Collection. A table of contents must be included at the front of the collection. The order of this table should be the same as the order in the collection. Order your collection as follows: 1-10 mounted specimens; 11-30, additional collection specimens turned in on newspaper; 31-50 extra credit specimens. Remember to include 5 grasses in your first 30 specimens.

Pressing and Drying

The following points will aid the student in obtaining durable plant specimens.

1. Place plant specimens between several pages of newspaper or other similar absorbent paper.
• Large plants can be bent once or twice so as to fit on the page.
• Expose the underside of several leaves so that characteristics of upper and lower surfaces will appear.
• Roots should be spread to expose them to their utmost.
• Large plant parts such as fruits, stems, and roots should be cut in half or sectioned.
• Seed samples collected should be placed in a cellophane bag and saved for mounting later.

2. Place the plant specimen in a press or under weights with alternate newspaper sheets and absorbent material (cardboard blotters).
• This aids in absorbing moisture from green samples.
• Change the newspaper and blotters as often as needed (at least once a day at first). Extremely fleshy plants are hard to preserve and the paper may need to be changed 2 or 3 times a day. Blotters or dryers: —these should preferably be large blotters of a similar size t the half sheets of newspaper for plant folders. If blotters are not available, dryers of newspaper can be made. These would consist of about 1/4 inch pad of newspaper taped together into a pad the size of the plant folders. Many of these will be needed. The most common mistake is not changing the absorbent material often enough. Moldy and discolored specimens show up rapidly under moist conditions.
• Two press boards are needed, one for each side of the press. These can be sheets of 3/8 or 1/2 inch plywood cut to the same size as the plant folders. Two straps, belts, or ropes are needed to put around the entire press to hold it together and apply pressure. Weights on the press could be used. If press boards are not available, place the prepared specimens (see item 1) between layers of absorbent material on a flat surface. Place weights (books do nicely) evenly on top of the stacked specimens. Make sure you do not stake too many plants in this manner in order to insure thorough drying of the specimens.
3. Pressing and drying is very important. If care is not taken, the entire quality of the specimen can be ruined. A plant just wadded up in the middle of some newspaper will result in a poor specimen. Part of the collection credit comes from sample quality.
4. Dried plants can be stored in a cool dry place. By leaving them in a folded newspaper page they can be moved easily. Remember that these dry plants are brittle and will break easily. Specimens which are not mounted will be turned in inside the folded newspaper.

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Weed ID

References

Weeds of the West, Western Society of Weed Science

Weed ID Guide, Southern Weed Science Society

An Illustrated Guide to Arizona Weeds

Weeds and Poisonous Plants of Wyoming and Utah, T. D. Whitson ed.

Arizona Flora, T. H. Kearney and R. H. Peebles

Weed Control Manual and Herbicide Guide, 1994

Links

Weed Seedling Identification

NMSU weed links

UCDavisLinks

IAState

Cornell ID

Colby ID

Texas ID