Botany Blog Plants of the Northeastern U.S.

March 22, 2012

Monarch Butterfly Populations Declining

The larvae of Monarch Butterflies (Danaus plexippus) feed exclusively on plants in the genus Asclepias (Milkweeds) and a few other related genera.

Monarch caterpillar on butterfly weed

Monarch larva on Butterfly Weed (Asclepias tuberosa)

According to a new study published in the journal Insect Conservation and Diversity (Pleasants & Oberhauser, 2012), overwintering monarch butterfly populations in Mexico have declined by about half since 1999. This is correlated with an estimated 58% decline in milkweed populations in the Midwest and a corresponding decline of 81% in monarch breeding success. These effects are most likely due to the widespread use of Glyphosate on genetically modified crops immune to the herbicide (i.e. Roundup Ready crops).

April 3, 2011

Utricularia sandersonii

Filed under: Plant-Insect Interactions — admin @ 23:37

I bought a couple tropical terrestrial bladderworts a few months ago and they have been spreading through my carnivorous plant collection since. They seem to like any spot with a little bit of water. One of the smaller ones, Utricularia sandersonii, bloomed for the first time the other day. It is a carnivorous plant native to South Africa with flowers that are relatively large compared to the tiny leaves.

Utricularia sandersonii

The upper petals have been described as looking like “bunny ears”, although they are not very distinct on this plant.

Flower

View of the flowers from the side. Note the long spur.

Side view of flower

January 30, 2011

Sundews

Eastern North America has a few endemic sundews (Drosera spp.), all of which occur in acid habitats like bogs. The most common in New York State is the round-leaved sundew (Drosera rotundifolia). It has round leaves (obviously!) that are covered with stiff glandular hairs each tipped with a sticky drop of “dew”. The leaves are often a bright red which serves to attract insects, and the sticky glands trap the insects. After capturing an insect the leaf usually folds inward to increase surface contact and digestion occurs with the aid of enzymes secreted by the leaf.

Round-leaved Sundew

A species with more elongate leaves that also occurs in our area in the narrow-leaved sundew (Drosera intermedia). I found this specimen growing along one of the rivers that runs through the New Jersey Pine Barrens. The thread-leaved sundew (Drosera filiformis) also occurs in the Pine Barrens and it has much longer and narrower leaves. I have not yet found this latter species growing in the wild and it is quite rare in NY.

Narrow-leaved sundew

A popular subtropical sundew for terrarium culture is Drosera tokaiensis from Japan, which is a natural hybrid of D. rotundifolia and D. spatulata. It is easy to grow from seed and does not require a period of dormancy like our temperate sundews.

Drosera tokaiensis

 

Sundews can be grown under the same conditions as the Venus Flytrap.  A mixture of peat and sand works well for the substrate. Ambient conditions should be kept humid and only distilled water should be used. Bright light will bring out the best color. Plants grown in moderate light will tend to be more green, and plants grown in low light may decline over time. When growing temperate sundews the plants may form a tight rosette late in the growing season and this is an indication that they are going dormant. Such plants can be placed in a refrigerator for several months to break dormancy.

August 29, 2010

Purple Bladderwort

Bladderworts are carnivorous plants that form tiny bladder-like traps capable of capturing small organisms. Most species in the Northeastern U.S. are aquatic but a few species are terrestrial. Purple Bladderwort (Utricularia purpurea) is an aquatic species that occurs in soft, quiet waters of the Atlantic coastal states and sporadically further inland. It flowers from July to September.

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February 8, 2010

Eastern Comma

Filed under: Plant-Insect Interactions — admin @ 22:25

Spring semester is in full swing so it has been difficult to find time to write of late. I shot this image of an Eastern Comma (Polygonia comma) last summer as it was resting on a bench along the boardwalk that leads into a poor fen here in central NY.

Eastern Comma

This butterfly occurs throughout most of the eastern half of the United States and has two broods a year. The larvae will feed on a variety of host plants including False Nettle (Boehmeria cylindrica), Wood Nettle (Laportea canadensis), American Elm (Ulmus americana) and Stinging Nettle (Urtica dioica). Adults feed on the sap of trees (Layberry et al. 1998).

Literature cited:

Layberry, R.A., Hall, P.W., and Lafontaine, J.D. 1998. The Butterflies of Canada. University of Toronto Press.

January 17, 2010

Passiflora x belotii

Filed under: Plant-Insect Interactions — admin @ 02:31

Passiflora x belotii is the name given to the hybrid of P. alata and P. caerulea. It is a sterile hybrid that will not produce fruit but is a prolific bloomer when given plenty of light. The flower shown here was taken from one of my plants that was erroneously labeled P. incarnata at the nursery where I bought it.

Passiflora x belotii

There are over 450 recognized species in the genus Passiflora (Vanderplank 1996). Most are vines, but a small number can grow as trees (e.g. P. lindeniana). Most people recognize passionflowers as having purple and white flowers, but there are species that produce white, pink, yellow, red and even orange flowers. The flowers of the hybrid shown here are very fragrant with a scent similar to that of the fruit of P. edulis. The foliage of passionflowers is toxic primarily due to the presence of cyanogenic glycosides. When a leaf is chewed by an insect, these glycosides interact with ezymes in the leaf (much like when a glow stick is “broken” allowing the chemical components to mix) and release hydrogen cyanide as a by-product. A group of tropical and subtropical butterflies (subfamily Heliconiinae) have co-evolved with plants in the genus Passiflora and have developed the ability to somehow metabolize these compounds and use them as a defense against predators (Engler et al. 2000).  One of the better known species is the red postman butterfly, Heliconius erato, which is often displayed in butterfly houses at botanical gardens and nature centers.

Heliconius erato

This image was taken at Hershey Gardens in their butterfly house. It is worth noting that the garden does not breed or raise their butterflies; they purchase pupae from places in the tropics that rear caterpillars, some of which are sold while others are released back into the wild to aid conservation efforts in areas where suitable habitat is diminishing.

Engler, H.S., Spencer, K.C. and Gilbert, L.E. 2000. Insect metabolism: Preventing cyanide release from leaves. Nature, 406, 144-145.

Vanderplank, J. 1996. Passion Flowers, 2nd ed. The MIT Press. Cambridge, MA.

December 18, 2009

Venus flytrap

Here are some of the “traps” of a venus flytrap, each consisting of a bi-lobed leaf at the end of a flattened petiole. They are active traps, meaning that they are capable of closing quickly to ensnare a prey item. Each lobe of the trap is beset with three large trichomes (the trigger hairs), readily visible in the image below. If any two of the hairs are touched, or if one of them is touched twice, this will cause a rapid pressure change within the cells and trigger the trap to close. The long segments along the edge of each lobe may look like sharp teeth but they are quite soft to the touch; they serve to prevent the escape of the prey, not to impale it.

Venus Flytrap

Venus flytrap (Dionaea muscipula) is a very popular plant, mostly owing to its ability to actively capture and digest insects. It has become widely available now due to the ease by which it can be propagated using tissue culture. Unfortunately many who attempt to grow this plant fail due to a lack of understanding of its cultural requirements. Understanding how to successfully grow this plant begins with understanding where it comes from and why it captures bugs in the first place.

Venus flytrap is the only species in its genus. It is in the family Droseraceae, which includes another group of carnivorous plants known as sundews (Drosera spp., e.g. Drosera rotundifolia). Unlike sundews, the venus flytrap has a much more limited natural range, originally found only in a small area of southern North Carolina and northern South Carolina. The natural habitat of this plant is open, acidic wetlands on peaty or sandy soils with low nitrogen availability. The capture and digestion of insects is an adaptation to these nitrogen-poor environments, allowing the plant to break down proteins and absorb the nitrogen for use in metabolic functions.

One mistake people make in trying to grow this plant is not providing it with sufficient humidity. Dry air causes the leaves and the traps to dry out and turn black. A glass or plastic cover satisfies this requirement; a small gap in the cover should exist to allow for some air circulation. Watering can be accomplished by standing the pots in shallow water. Distilled water is best, as hard water or water containing various salts (this would include softened water) will eventually kill the plant. While the plants can stand being in soil that is completely saturated for short periods, it is best to avoid this.

The question I am most often asked is if it is necessary to feed them. Not really, at least not as often as some would think. It is also best to feed the plants insects and not hamburger, although lean meats will work. I prefer to either set plants outside for a time in the summer to allow them to capture insects naturally or give a light dose of fertilizer to the leaves.

Lastly, there is the issue of dormancy. Venus flytrap occurs in temperate areas of the southeastern United States that experience occasionally low temperatures as low as 5 degrees F in the winter. In nature they go dormant in the fall as day lengths shorten and temperatures begin to fall. If plants are grown under natural light, as would be the case with a plant growing on a windowsill or outside, they must be allowed to go dormant and remain in that state for several months. Such plants could be kept in a refrigerator for that time. All of my plants, including those pictured here, have never been allowed to go dormant and continue to grow vigorously. I think the key to my success has been the use of artificial lights set on a long-day cycle and not allowing temperatures to fall below 60 degrees F. While my plants never go dormant they still manage to bloom occasionally. I usually cut the blooms to reduce the energy cost to the plants though.

Venus Flytrap Flowers

October 1, 2009

Baltimore Checkerspot

Filed under: Plant-Insect Interactions — admin @ 18:31

Baltimore Checkerspot

This series of images shows the life cycle of the Baltimore Checkerspot (Euphydryas phaeton), one of the many brush-footed butterflies (family Nymphalidae) native to the northeastern U.S.  These butterflies have one brood per year. The larvae are sometimes said to feed exclusively on the plant shown in the last frame, White Turtlehead (Chelone glabra), but I have found the larvae feeding on Purple False Foxglove (Agalinis purpurea) and Common Valerian (Valeriana ciliata) as well.

September 27, 2009

Dispersal of Trillium seeds by ants

Filed under: Plant-Insect Interactions — admin @ 19:13

Tug of war

I have put together this blog as a supplement to my main website, www.thismia.com, which is devoted to native plants of the Northeastern United States. This first entry is about my observations of ants dispersing seeds in a deciduous forests of the northeastern U.S. This was part of a pilot study that was eventually designed to measure the frequency of ant dispersal of Trillium seeds in post-agricultural forests.

There is a large, lipid-rich structure called an elaiosome attached to the seeds of Trillium spp. which serves to attract ants (when ants disperse plant seeds this is known as myrmecochory). This structure also attracts ground beetles, slugs, and sometimes yellow jackets. In the case of beetles and slugs, the elaiosome tends to be consumed in place and the seeds do not get dispersed. Also, after the elaiosome is consumed ants will no longer gather the seeds. It is likely that seeds which have the elaiosome removed will germinate close to the parent plant, and this has been confirmed by seed exclosure experiments using seed of Erythronium americanum (Wein and Pickett 1989). Ants disperse nearly one-third of herbaceous woodland angiosperm seeds (Beattie and Culver 1981), and therefore short-distance dispersal that could expand local plant populations may be limited by ant activity. Ants have been shown to disperse the seeds of myrmecochorous species (e.g., Trillium grandiflorum (Michx.) Salisb.) only < 2.4 m away from parent plants in a single year. Occasional long-distence dispersal by yellow jackets may be important for the eventual recolonization of Trillium and other ant-dispersed plant species in secondary forests. Most of the time yellow jackets do not disperse Trillium seed much further than ants do, but can occasionally disperse seeds more than 20 meters from the parent plant (Zettler and Spira 2001).

The image is of ants dispersing Trillium erectum seeds that were placed on a rock in a forest in central NY. A previous seed sowing experiment conducted in Denmark had reported an absence of ants within secondary forests (Petersen and Philipp 2001). I was ultimately urged to remove this study from my thesis but I was able to demonstrate that ant activity was quite high in secondary forests in central NY, and possibly higher than ant activity in primary forests in the region.

Works Cited

Petersen, P.M. and M. Philipp. 2001. Implantation of forest plants in a wood on former arable land: a ten year experiment. Flora 196:286-91.

Wein, G.R. and S.T.A. Pickett. 1989. Dispersal, establishment, and survivorship of a cohort of Erythronium americanum. Bulletin of the Torrey Botanical Club 116:240-246.

Zettler, J.A. and T.P. Spira. 2001. Yellow jackets (Vespula spp.) disperse Trillium (spp.) seeds in eastern North America. American Midland Naturalist 146:444-446.

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