How to Press and Mount Aquatic Plants

Materials Needed:

Plant Press* - may be purchased or built. It consists of alternate layers of corrugated cardboard, absorbent (blotting) paper or newspaper, and equal-sized pieces of plywood with straps or some other method of applying even pressure.

Pencil and Waterproof Paper - for making notes on site. 

Herbarium Paper* - acid-free, 100 percent rag paper is best. If you would rather buy paper locally, try to use heavy stock, relatively acid-free paper with high rag content. High-grade thick typing paper will work and you can generally purchase this at quality stationary stores, or university bookstores typically sell biology paper that is good quality 81/2 by 11 inch white paper.

Packets* - for extra plant structures (like seeds), use small envelopes or a piece of folded  paper (2 x 3 inches).

Herbarium Paste* - available from biological supply companies. White glue can also be used (should have a polyvinyl acetate base).

Linen Tape - Bookbinders tape is best. Avoid cellophane tapes. 

Labels* - See the sample label at the end of the article for an example of a completed label. Size labels to fit in the lower right corner of the herbarium paper. 

*These items are available from biological supply companies.

Collect the Plant 

Collect as much of the plant as possible: Include roots, stems, leaves, flowers, and fruits. Plants may be collected by hand pulling, or using a weighted rake to gather plants in deeper water. 

Write as much information about the plant as possible on the notepaper (you will use the information for aid in plant identification and for labeling the plant). Include the date; collector's name and address; location (name of waterbody as well as the location of the waterbody); depth of water; flow rate of  water; substrate (sediment) description; whether leaves and/or flowers are submersed (below the water surface), floating, or emergent (above the water surface); color and odor of flowers; and names of the plant  species associated with the collected plant. 

Wash the plant in clean water to remove algae, debris, and sediment. Keep the plants moist until you can press the plants.

Press the Plant 

Note: It is easiest to identify aquatic plants before pressing. If this is not possible, press the plant while it is fresh, and then send it to an aquatic plant expert as instructed below.

Prepare the plants for pressing:

For delicate submersed plants, the best method is to float the plant onto a sheet of paper (newspaper or a heavy stock paper will work, or you can float the plant directly onto the herbarium paper). You can do this by placing the plant in a pan of water with the paper below it. Position the plant on the paper and hold it in place with a finger. Slowly lift the paper and plant from the water. The water flowing from the paper should separate the leaves while the plant adheres to the wet paper. Cover the plant with newspaper or absorbent paper. (If the plants tend to stick to the paper, you can cover them with wax paper on one side). 

When pressing plants with whorled or finely divided leaves, it is useful to separate one  node (the stem section where the leaves are attached) and float that onto a small portion of the paper. This yields a cross section showing the leaf pattern.

For plants with large bulky stems, roots, or leaves, split the bulky portion before pressing to facilitate drying and to prevent uneven pressure in the press.

If you collect extra flowers, fruits, or vegetative parts, press them, dry them, place them in packets, and glue the packets to the herbarium paper. 

Press the plant material by placing the plant between two sheets of newspaper or absorbent paper then sandwiching this between two sheets of corrugated cardboard. Several prepared specimens can be stacked in this manner (label or number the plants so you know which plant matches which field note). Then, put the stack between two firm pieces of wood and apply an even pressure using straps, bolts, or a heavy weight. Place in a warm, dry area. To avoid mildew, change the newspaper periodically until the plants are dry. The plants will dry faster if placed over a heat register, fan, or incandescent light bulbs. 

Mount the Plant

Note: To verify the specimen identification (if necessary) send a duplicate pressed, but unmounted specimen with a complete label to an authority on aquatic plants. They will keep this specimen for their collection and notify you of the plant's name. Be sure the two specimens are of the same species. 

Once the plant has dried and is identified, it is mounted and kept for future reference. 

Arrange the plants on a piece of herbarium paper. If the plant is too long, you may cut it into several sections and place it lengthwise on the paper.

Either glue or tape the specimen to the paper (the use of glue or paste will sometimes tend to cause delicate submersed plants to curl; tape may be preferable in such cases). 

Complete a label with the plant's Latin (scientific) name, location, and site description, name of the collector, and the date collected. Attach the label to the lower right corner of the paper. 

If you collected additional reproductive parts (seeds, fruits, flowers) or vegetative parts, place these in the packet. Glue the packet to the top of the herbarium paper so you can access the contents. 

Take care to ensure that insects do not damage the specimens. Store mounted plants with an insecticide or repellent (mothballs) to prevent colonization by insects. 

Example of a Sample Label:

Washington State Department of Ecology Herbarium
Olympia, Washington

Plant Name Sparganium eurycarpum
Location PACIFIC COUNTY: T14N R11WSO4. Tidal area 5.5 miles south of the Pacific and Grays Harbor County Line on Highway 105. Growing in wet soil between drift logs above the beach with Carex obnupta and Oenanthe samentosa
Collector's Name E. Burnett
Date July, 1991 

For more information about collecting and pressing plants, contact Jenifer Parsons at jenp461@ecy.wa.gov.