Keeping A Dead Leaf Partly Alive
If you look on the ground these days as yellow Trembling and Bigtooth Aspen leaves are falling, you may notice that small splotches of green remain in some of them. These chlorophyll-laden patches are usually found near the bottom of the midrib of the leaf. If you open the pocket of tissue at the base of the green section, it’s highly likely you will find a minuscule (2 mm long) translucent caterpillar (a microscope may be necessary to detect it).
The caterpillar (larva) first bores into the stem, or petiole, resulting in a swelling. When it reaches the leaf blade it makes an elongated blotch between the midrib and the first lateral vein. The larva is capable of secreting a chemical which prevents the natural deterioration of the leaf. As a result, chlorophyll is retained in this area and photosynthesis continues to take place, providing the larva with food. The leaf-mining larva (Ectoedemia sp.) will pupate over the winter (outside the leaf) and emerge next spring as a very tiny moth which will feed on the honeydew secreted by aphids. (Photo: Mined Bigtooth Aspen, Populus grandidentata, leaf)
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Evergreen Orchid Leaves Brighten The Forest Floor
Downy Rattlesnake Plantain (Goodyera pubescens) is a perennial evergreen orchid found growing in deciduous and coniferous forests, often in dry, sandy soil. While its hairy (downy) stalk of delicate, white, late-summer flowers is eye-catching (see 8/20/13 NC post), the leaves of Downy Rattlesnake Plantain are also works of art. Rosettes of bluish-green leaves emerge at the end of horizonal rhizomes, or stems, that are usually covered lightly by leaf litter.
The common name “plantain” has been applied to diverse, unrelated plants that have broad, flat leaves, the word being derived from the Latin word planta, referring to the sole of the foot. “Rattlesnake” alludes to the resemblance of this plant’s prominent reticulated veins to the scaly skin of snakes.
As is typical of orchids, the roots of Downy Rattlesnake Plantain have a mycorrhizal relationship with fungi that assists the plant in the acquisition of moisture and nutrients, while the plant provides products of its photosynthesis to feed the fungus. Also typical of orchids, the seeds of this species are minute and dust-like, bearing few nutrients to assist in the establishment of new seedlings. Seedling establishment requires assistance from soil fungi, from which the orchid derives the organic molecules it needs until it can make its own food via photosynthesis in its leaves.
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Oak Leaf Shapes & Sizes
There are roughly 90 species of oak trees in North America, several of which can be found in New England. (Eastern White, Northern Red, Eastern Black, Burr, Common Chinkapin, Swamp White, Pin, Chestnut, Bear, Scarlet and Common Post). When identifying oaks, several characteristics, such as buds, bark, branching pattern and leaves, can be used. Most Northeastern species of oak have lobed leaves, with the lobes deep or shallow, pointed or rounded.
One thing all oak leaves have in common is their variability. Even on a single tree, you can find leaves of widely differing shapes. One reason for this is that the amount of sunlight that reaches them affects their shape. Leaves that are shaded are not only often larger than those that are bathed in sunshine, but their lobes are far more shallow. Both of these traits maximize the intake of sunlight. Canopies of oaks have a larger proportion of small, deeply-lobed leaves than lower down on the trees, where you can often find relatively large leaves that appear to lack lobes completely. The two pictured leaves come from the same Northern Red Oak. Can you tell where on the tree they probably grew? (Thanks to Penny March for post idea and leaves.)
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Witch-hazel Cone Gall Aphids Laying Eggs
At this time of year there is a species of aphid, Hormaphis hamamelidis, that is laying eggs on Witch-hazel branches. Next spring female aphids will hatch out of these eggs and begin feeding on newly-emerged Witch-hazel leaves. The aphids inject the leaf with a substance that causes the leaf to form a cone-shaped growth, or gall, around the insect, providing it with both food and shelter. The galls are hollow, and have openings extending out through the leaves’ lower surfaces. Within the galls the unmated female aphids produce 50 – 70 young. Eventually the galls fill with winged female aphids which emerge through the cone openings, disperse, and repeat the process. The third generation of aphids consists of both males and females which mate and lay their eggs on Witch-hazel. The aphids that hatch from these eggs create the conical galls found on Witch-hazel leaves.
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Abscission Layers Forming
As the days grow shorter and the nights longer, cells near where a leaf’s stem joins a tree’s branch start to divide rapidly. This is the start of the creation of the corky layer of cells known as the abcission layer.
The annual growth of a tree ends with the formation of the abcission layer. This layer prevents the transport of materials such as carbohydrates from the leaf to the branch and it blocks the flow of minerals from the roots into the leaves. Chlorophyll, critical to the process of photosynthesis, breaks down with exposure to light and is replaced continually by the leaves during the summer. When the abcission layer forms, this is no longer possible. The chlorophyll slowly breaks down and disappears, revealing the underlying xanthophylls (yellow pigments) and carotenoids (orange pigments) that the chlorophyll was masking. These pigments, in addition to the red pigments (anthocyanins) that are manufactured from sugars trapped in the leaf, provide us with our brilliant foliage.
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Early Splashes of Maroon
At this time of year, our eyes are immediately drawn to the brilliant orange, red and yellow pigments of Sugar Maple (Acer saccharum) leaves. However, there’s much to be said about the less flamboyant splashes of color adorning some of the species of trees that provide New England’s spectacular fall foliage. One such subtley-colored fall tree that often grows in upland forests along with Sugar Maples is White Ash (Fraxinus americana). One of the first trees to change color in autumn, White Ash can turn shades of yellow, orange and red, but deep red, maroon and purple are typically the grand finale of this species. Often its leaves progress from green to yellow and eventually maroon. While it might not be the first tree that catches your eye, make a point of looking for its colorful, compound leaves – you won’t be disappointed.
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Woolly Oak Leaf Gall
Of the 2,000 kinds of galls found on North American plants, 800 different kinds form on oaks. One of these is the woolly oak leaf gall, produced by a tiny Cynipid wasp, Callirhytis lanata. This gall is usually attached to the mid-vein on the underside of an oak leaf, and looks like a ball of wool. It may be as large as three-fourths of an inch and is often bright pink or yellow in color, fading to light brown in the fall. Oak trees have lots of tannic acid in them (a defense which makes the tree unpalatable to herbivores), with the highest concentration found in oak galls. (The bitter taste is where the name “gall” originated.) It’s possible, since tannins are somewhat anti-microbial, high-tannin galls such as the woolly oak leaf gall may protect the larva against fungi and bacteria.
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Goldenrod Bunch Gall
Galls are abnormal plant growths that are caused by a number of agents, including insects. Each gall-making insect has a specific host plant and location (leaf, stem, bud) on which it lays its eggs in the spring, during the growing season. The egg-laying and/or hatching and chewing of the larva causes the plant to react by forming a growth around the insect. Galls of different species of insects vary in their shape and the gall maker can often be identified as a result of this.
Goldenrods are host to about 50 species of gall-making insects, two-thirds of which are midges, or tiny flies. Goldenrod Bunch Galls, also called Rosette Galls, are the result of an egg being laid in the topmost leaf bud of Canada Goldenrod, Solidago canadensis by a midge in the genus Rhopalomyia, often Rhopalomyia solidaginis. The stem of the goldenrod stops growing, but the leaves don’t. The resulting rosette of leaves provides shelter and food for the midge larva, as well as a host of other insects, including other midges. Adult Goldenrod Bunch Gall midges emerge from the galls in the fall, and females lay eggs in the soil. The larvae hatch within one to two weeks and spend the winter underground, emerging in the spring to start the cycle all over again. Interestingly, Rhopalomyia solidaginis lays all male or all female eggs, one or the other.
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Red-eyed Vireo Nest
Abandoned bird nests are evident now that leaves have fallen off the trees. Consider the time and effort that goes into the construction of one of these single-use nurseries. Take the Red-eyed Vireo’s nest you see here lying on the forest floor. The female selects a nesting site — a time-consuming task, as the requirements are that it conceal the nest and provide shade for her young. (Too much sun will cause her to abandon the nest. One female who had selected a sunny spot was observed pulling nearby green foliage over her nest and fastening it in place with spider webs.) The female vireo then collects nesting material for the three layers of her nest: Exterior – tree bark, spider-egg cases, wasp-nest paper, lichen, green leaves and pine needles. (Nests exposed to sunlight may be decorated with light-colored tree bark such as birch bark.) Interior – bark strips and plant fibers. Inner lining – grasses, pine needles, plant fibers and animal hair. She then weaves these materials into a cup-shaped nest that is suspended from a forked branch by its rim. A trip for materials is made every 3 – 11 minutes and roughly twenty seconds is spent working each load into the nest structure. This intensive work takes the female vireo approximately five days – all accomplished without the aid of any hands or tools, and she only uses the result of all this work once. Fortunately, recyclers make good use of her efforts.
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Pitcher Plants Turning Red
Pitcher plant leaves are primarily green in the summer, tinged with red, but as summer turns into fall, many become deep red. Although this red color was thought to attract insects, it appears that this is not the case. The color change, according to research cited in the Journal of Ecology, is due to the level of phosphorus this carnivorous plant has received from its insect meals. There is a limited amount of phosphorus in a bog and plants living there acquire it in different ways. The pitcher plant acquires phosphorus from insects that it traps. It then utilizes the phosphorus to revitalize the (green) chlorophyll in its leaves for photosynthesis. The deep red color that the leaves turn in the fall indicates that the plant has not had a good meal in quite some time.
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Poison Ivy Thriving
Poison Ivy is in the Anacardiaceae family, which also includes cashews, mangos and sumacs. The sap of the stems, roots, fruit and leaves of many species in this family contains urushiol oil, which is what causes the allergic rash in 80% of humans that come in contact with these species. Poison Ivy is very sensitive to carbon dioxide, and even slightly elevated levels of CO2 have proven to increase its growth. In the past 50 or 60 years, during which time the amount of carbon dioxide in the atmosphere has increased by roughly 22%, Poison Ivy’s growth rate has doubled. The amount of urushiol oil has not only increased, but it is also more potent…leaves of three, let them be.
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Deciduous Leaves Falling
The falling of a leaf is the final step in an ordered series of events referred to as senescence. This process allows trees to conserve resources, prepare for a dormant period, and shed inefficient tissues. When leaves become unable to produce food due to a lack of chlorophyll, a process of shutting-down and sealing-off begins. Leaves are shed through a number of biological actions which take place at the base of the leaf’s stem, or petiole. The walls of some cells weaken, while those of other adjacent cells expand. The expansion of the latter causes pressure against the weaker-walled cells, resulting in these two groups of cells tearing away from each other, causing the leaf to fall. The tree forms a protective barrier on the wound where the leaf had been attached to the branch, sealing it off from pests and the environment and leaving a leaf scar.
Sundews Capture Their Meals
Sundews (Drosera spp.) are carnivorous plants often found in acidic bogs, fens and cedar swamps. They have numerous small leaves arranged in a circular, or rosette, pattern and they are covered with reddish, glandular hairs, or tentacles, that exude a sticky secretion at their tips. Insects, attracted to the glistening sticky droplets which resemble dew, land on a leaf and become stuck. The movement of the struggling insect triggers cell growth in the glandular hairs and they begin folding over the insect within 60 seconds. An anesthetic is released by the plant’s hairs, causing the insect to become motionless. Digestive enzymes are then secreted which liquefy the insect’s internal organs so that they can then be absorbed by the plant’s hairs. Although insect prey is not vital to sundews, the nitrogen the plants receive from the insects enables them to thrive in environments where nitrogen is in short supply. The damselfly pictured has been captured by a Round-leaved Sundew’s glandular hairs which have rendered it motionless and have started to grow and fold over the tip of the damselfly’s abdomen and its wings.
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A Great Christmas Present!
If you’re looking for a present for someone that will be used year round, year after year, Naturally Curious may just fit the bill. A relative, a friend, your child’s school teacher – it’s the gift that keeps on giving to both young and old!
One reader wrote, “This is a unique book as far as I know. I have several naturalists’ books covering Vermont and the Northeast, and have seen nothing of this breadth, covered to this depth. So much interesting information about birds, amphibians, mammals, insects, plants. This would be useful to those in the mid-Atlantic, New York, and even wider geographic regions. The author gives a month-by-month look at what’s going on in the natural world, and so much of the information would simply be moved forward or back a month in other regions, but would still be relevant because of the wide overlap of species. Very readable. Couldn’t put it down. I consider myself pretty knowledgeable about the natural world, but there was much that was new to me in this book. I would have loved to have this to use as a text when I was teaching. Suitable for a wide range of ages.”
In a recent email to me a parent wrote, “Naturally Curious is our five year old’s unqualified f-a-v-o-r-I-t-e book. He spends hours regularly returning to it to study it’s vivid pictures and have us read to him about all the different creatures. It is a ‘must have’ for any family with children living in New England…or for anyone that simply shares a love of the outdoors.”
I am a firm believer in fostering a love of nature in young children – the younger the better — but I admit that when I wrote Naturally Curious, I was writing it with adults in mind. It delights me no end to know that children don’t even need a grown-up middleman to enjoy it!
Downy Rattlesnake-Plantain
If you look at the forest floor in coniferous woods you may well discover Downy Rattlesnake-Plantain (Goodyera pubescens ). This evergreen rosette of broad, rounded leaves gets its name from the similarity of the shape of its leaves to those of plantain, a common lawn weed. In fact, it is an orchid, not a plantain, and is the most common species of plantain in New England. It is distinguished from other species of rattlesnake-plantains by the bright silver markings on the leaves and the broad stripe down the center of the leaves. Each leaf lasts for approximately four years.
Virginia Creeper
As you might assume from its appearance, Virginia Creeper (Parthenocissus quinquefolia) is in the Grape family. This climbing woody vine clings to the surfaces over which it climbs with adhesive disk-tipped tendrils, which are actually modified flower stalks. The disks form only after the tendril has made contact with a tree or other surface, at which point the disk secretes a cement-like substance, keeping the vine attached to the substrate long after it has died. Although it superficially resembles poison ivy, Virginia Creeper has five leaflets (“quinquefolia”), as opposed to poison ivy’s three. Virginia Creeper’s brilliant red fall foliage is thought to attract birds, which consume the blue-black berries and disperse the seeds.
Leafcutter Bee Cell
Congratulations to those who recognized yesterday’s Mystery Photo! The tiny green cells are made from the leaves of almost any deciduous trees, and are cut and folded by leafcutter bees (Megachile genus). These solitary bees are about the size of a honeybee, but are much darker, almost black. They construct cigar-like nests (often in soil, holes in wood made by other insects, or plant stems) that contain several cells. After gathering and storing a ball, or loaf, of pollen inside the cell, the bee lays an egg and seals the cell shut. When the egg hatches, the larval bee feeds on the pollen and eventually spins a cocoon and pupates within it. An adult bee emerges from the cocoon and usually overwinters inside the cell. In the spring the bee chews its way out of the cell. Leafcutter bees pollinate wildflowers, fruits and vegetables and are also used as pollinators by commercial growers of blueberries, onions, carrots and alfalfa. (Photo submitted by Jan Gendreau.)
Blue-eyed Grass
It’s easy to miss Blue-eyed Grass (Sisyrinchium angustifolium), as its flower is only about ½” in diameter and the plant only reaches a height of six to twelve inches. Blue-eyed Grass is a member of the Iris family, not, as its name implies, a member of the Grass family, although it does have stiff, grass-like leaves. Dark lines on its petals and sepals may well serve as nectar guides, leading pollinators to the yellow center. Each blossom is open for only a day at most. Typically you find Blue-eyed grass growing in sunny, wet fields, often on elevated soil — Thoreau noted that if you followed Blue-eyed Grass through a wet meadow, you could keep your feet dry.
Full Moon
Newly-emerged Sugar Maple leaves in last night’s full moon.
Delayed Greening of Young Leaves
Many plants practice “delayed greening” of their leaves, including this Red Maple (Acer rubrum). An initial lack of chlorophyll prevents the leaves from photosynthesizing and making food, which means they have little nutritive value, and thus, appeal, to an herbivore. Most plants that delay greening have reddish leaves due to the presence of anthocyanin, a pigment which appears reddish. A majority of herbivorous insects and invertebrates cannot detect colors in the red range of the color spectrum. Young leaves suffer the greatest predation from invertebrate herbivores. Red leaves would be perceived by these leaf eaters as somewhat dark and possibly dead – not a choice food material. It is possible that the red coloration of new leaves allows the plant to make them unappealing to the herbivores that would otherwise eat them.
Naturally Curious with Mary Holland 
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