Trailing arbutus (Epigaea repens) has just started blooming in Central NY. It is a member of the Heath Family (Ericaceae) found in semi-open areas on acidic, mesic to dry, sandy or gravelly soils. It seems to prefer slopes, perhaps because on level ground the evergreen leaves would otherwise covered by falling leaves from the canopy above. It can be locally abundant and has a NY state rank of S4.
May 2, 2015
February 28, 2011
I am in the process of digitizing and cataloging the vascular plant specimens housed in the herbarium at SUNY Cortland. Some of the specimens were not mounted properly or demonstrate other issues that may not have been obvious to the collector at the time. The purpose of this article is to describe a few of these issues and explain how to avoid them to improve the longevity of mounted plant specimens.
A standard herbarium sheet is 11.5 x 16.5 inches. Larger sized sheets do not fit properly into a folder and are prone to damage, and are also prone to damage other specimens as they jostle the other contents of the folder in which they are stored.
A 100% rag content sheet is optimal but 25-50% rag paper can be used. Of greatest importance is that it be acid-free. Not only will an acid paper deteriorate over time, but it will also damage any specimens that it comes into contact with. Below is an example of such a sheet that was damaged by a smaller sheet placed on top of it. You can see the damage as a darker rectangle in the lower left of the sheet.
Another problem with some of the specimens was the use of inappropriate mounting materials like scotch tape. The degree of deterioration varies. The plastic tape used to affix the label on the specimen below can be seen to have degraded badly and darkened the paper of both the herbarium sheet and label to a large extent.
If tape is to be used to help fix the specimen to the sheet it should be acid-free gummed linen tape. Some art suppliers carry this archival tape. Only thin strips are used and potentially the tape could be removed at a later date by re-softening the adhesive with water. The following image shows the tape used to mount a specimen that is now over 100 years old. As you can see it is still in excellent condition, however the paper on which it was mounted was not of the best quality so it has darkened quite a bit.
A final note regarding adhesives. The one most often used is polyvinyl acetate glue like “white glue” (Elmer’s). White glue is sensitive to heat and moisture and will degrade in UV light, but these should not be an issue in a properly maintained herbarium. I have found that when other, unknown adhesives had been used that they had turned brown, became brittle, and the specimen or label it was used to mount had fallen off. When using white glue it is usually diluted with a small amount of water (less than the amount of glue or it will be too thin), and dabbed gently onto the specimen with a paintbrush. After gluing the specimen and label onto the paper the entire sheet should be covered with wax paper and gently pressed and left to dry overnight. The latter step assures the best contact with the sheet and keeps the specimen and paper from curling as it all dries. Bulky specimens can be further reinforced with a little thread sown through the paper and around the stem. As evidenced by the plants in our collection a properly mounted a specimen will last for at least a century.
And don’t forget to include relevant information on the label. I have come across far too many specimens lacking dates and complete location information. Without these a specimen is largely useless for scientific study.
December 22, 2010
With Christmas just a few days away I figured it would be a good time to discuss some of the plants often associated with the holiday. Besides trees, probably the one that most often comes to mind is the poinsettia (Euphorbia pulcherrima). The poinsettia is native to Mexico and South America. It is a member of the spurge family (Euphorbiaceae), many members of which produce milky latex sap and showy bracts (modified leaves) that surround one or more floral structures called cyanthia. A cyanthium is composed of a single female flower partially surrounded by a cup-like involucre topped by five simplified male flowers. In the poinsettia the cyanthia are yellow-green and the floral bracts resemble the leaves but are large and scarlet red.
A long-standing myth is that the poinsettia is poisonous due to the death of a 2 year old child in 1919 that was falsely attributed to ingestion of this plant. While the plant is not considered edible, the toxicity of the plant is quite low and at worst it may cause upset stomach or vomiting if eaten.
Another popular plant this time of year is the Christmas Cactus, which is actually represented by a few species mostly in the genus Schlumbergera. In the wild they are epiphytic cacti, growing on trees in forests of South America. What appear to be leaves are actually flattened stems. Sections of the stem root easily in a loose potting mix that includes a good proportion of sand. Flowering is triggered by short days and long nights, as is the case with poinsettia. While I don’t have any pictures of the latter, I did manage to find a few pictures of a Christmas Cactus in bloom.
I will end this with a perhaps less commonly known plant associated with the holiday, and one that is native to Eastern North America. The Christmas Fern (Polystichum acrostichoides) is so named because it was once popular for use in Christmas decorations due to its tough, evergreen leaves that can be found throughout the year, even under snow. It grows on well-drained soils in rich, shady woodlands.
July 18, 2010
Bittersweet Nightshade (Solanum dulcamara) is an herbaceous vine in the potato family (Solanaceae). It is native to Eurasia but has naturalized widely in North America. It occurs in a variety of habitats provided sufficient light is available. Several features aid in identification. First are the purple flowers with five reflexed petals and bright yellow stamens
The fruit matures from green to yellow, orange, and finally bright red and resembles a small tomato (also in the potato family). The plant gets its name from the reputed taste of the fruit, which is said to be bitter at first but later sweet. While the fruits are said to be less poisonous than the rest of the plant, I have never dared to taste one as all parts of the plant contain solanine which is extremely toxic. While poisonings are rare, fatalities have been known to occur.
The leaves are somewhat arrow-shaped and often have two or more lobes at the base. The color is dark green and they seldom have evidence of herbivory. The smell of the leaves is perhaps this plant’s most distinguishing characteristic, similar to tomato but much more foul and disagreeable. This trait has come in handy when it has been necessary to identify seedlings in the field.
July 5, 2010
Study plants for any length of time and one will eventually hear the phrase “sedges have edges”. This is because the stems of sedges typically have three angles, distinguishing them from the terete (round in cross-section) stems of grasses. For quite some time that was about the extent of my knowledge of this group of plants. A few years ago I decided to get serious about learning sedges, particularly the species rich genus Carex. One characteristic of plants in this genus is that the achene (seed) is surrounded by a sac known as a perigynium (plural perigynia). Close examination of these structures and the scales subtending them is often key to proper identification of plants in this genus. The perigynia are relatively large and inflated in Shining Bur Sedge (Carex intumescens), shown below.
Recently I have been adding photographs and descriptions for Carex species to my Plants of the Northeastern U.S. website. One goal has been to document important details of the inflorescence using a dissecting scope including a ruler marked in millimeters. Recently added pages include those for Carex brunnescens, C. debilis, C. deweyana, C. disperma, C. hystericina, C. interior, and C. radiata.
June 27, 2010
Poison hemlock (Conium maculatum) is a biennial herb that can grow to 3 m tall. It has a smooth stem that is often purple-streaked or spotted. The leaves are broadly triangular and divided into 3-4 segments with finely divided leaflets.
The white flowers are produced in umbels up to 6 cm wide and rather resemble a large Wild Carrot (Daucus carota).
This species is native to Eurasia but has been introduced and has spread widely throughout North America. Most often found in partially shaded, disturbed areas on soil ranging from dry to wet, it is perhaps best known as the plant given to Socrates after he was sentenced to death. All parts are extremely poisonous but the parts of the plant that are most toxic are the seeds and root.
May 3, 2010
Flowers can be characterized based on the position of the ovary in relation to the other parts of the flower. When the floral parts arise from a position below the ovary, the flower is said to be hypogynous (hypo=below; gynous=female) and the ovary superior since it is above the point where the other floral parts are inserted. When the floral parts arise from a position above the ovary, the flower is said to be epigynous (epi=above) and the ovary inferior since it is below where the other floral parts are inserted.
There is another, special case of an inferior ovary where the bottom of the sepals, petals, and stamens are fused into a cup around the ovary called a hypanthium, or floral cup. Such a flower is termed perigynous (peri=around), because the hypanthium surrounds the ovary. The presence of a hypanthium is a characteristic feature of some families of plants, particularly the Rosaceae and Grossulariaceae. I had a few minutes to kill today and decided to dissect a hyacinth flower that was in the lab and to my surprise found that Hyacinthus orientalis also has a perigynous flower. Here is a closeup of an entire flower
Flower cut in half longitudinally (below)
One last image after the ovary was removed so that the insertion of the stamens at the top of the hypanthium is more clearly visible. Also note the drop of nectar near the base of one of the filaments.
April 10, 2010
One of the more attractive trees in flower now in central NY is red maple (Acer rubrum). It is common in acid woodlands and swamps and has perfect flowers that range from yellow to red.
March 10, 2010
I have been experimenting with creating videos of plants lately. This one was shot using a webcam and it worked reasonably well.
This is an example of a nastic response to a stimulus. Specifically it is thigmonasty, a non-directional response to touch or vibration. The leaf of a venus flytrap is divided into two lobes, each of which bears three trichomes (hair-like structures). The closing of the “trap” is triggered by touching one of the little trigger hairs twice or by hitting two of them in succession. Somehow this causes a change in turgor pressure in the cells of the leaf and a rapid change in shape, allowing the trap to close rapidly.
February 24, 2010
Plant cells rely on internal hydrostatic pressure to maintain their shape. This pressure is maintained by a relatively high solute concentration inside the vacuole, which results in the absorption of water from outside the cell via osmosis (Raven et al., 2007). As the vacuole swells with water, the protoplast increases in size and the plasma membrane pushes up against the inside of the cell wall, resulting in turgor pressure. The turgor pressure is counteracted by the call wall and these opposing forces help maintain the shape of the cell and ultimately support herbaceous plant tissues.
The image below show cells in a leaf of Elodea canadensis that was placed in a solution of distilled water. The small green structures are the chloroplasts inside the cells and notice that they are distributed near the cell wall.
Elodea cell in a solution of distilled water
If a plant does not receive sufficient water or is placed in environment that is hypertonic (one that has a higher solution concentration than the plant cells, e.g. a salty environment), than the cells will lose water and the plants will wilt. This is because water will be drawn out of the vacuole through osmosis, the protoplast will shrink, and the plasma membrane will actually pull away from the cell wall (plasmolysis), resulting in a loss of turgor pressure.
The following image shows an Elodea leaf that was placed in a 20% sucrose (sugar) solution. Note how the inside of the cell is shrinking and the gap between the plasma membrane and the cell wall (the cell wall does not shrink because it is somewhat rigid due to the presence of cellulose microfibrils).
Elodea cell in a solution of 20% sucrose
Raven, P.H., Evert, R.F., and S.E. Eichhorn. 2007. Biology of Plants, 7th ed. Worth Publishers, Inc., NY.