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Sex Lives of Woodland Herbs Spring in the forest begins with a smorgasbord of flowering herbs. Hillsides become carpeted in white, pink, and maroon as open. The yellow bell-shaped flowers and mottled of trout lily blaze in the April sunlight. Yellow, white, and blue violets in profusion along trails and creeks. Squirrel corn (Dicentra canadensis) flowers flavor the air with a sweet aroma (Figure Spring Ephemerals). The early woodland herbs, or spring ephemerals, spring forth quickly with leaves, flowers, and and then wither just as summer heats up. Their strategy is to perform energy demanding activities quickly while sunlight abounds under the bare forest . In a few short weeks, many of these perennials will shift from a cryptic underground phase to a robust with conspicuous flowers only to return to hiding by July. The above ground growth phase is never prolonged. April trillium flowers progress to fruits and in late July. Trout lily (Erythronium americanum), on the other hand, has one of the shortest above ground periods. They send both leaves and flowers to the surface in early April, then six weeks later the plant senesces as the lies quietly on forest soil. Special contractile , common among lily members, pull the expanding trout lily corm further beneath the soil. The large, colorful spring ephemeral flowers advertise their and rewards to early flies and bees in the forest. Insects are efficient and abundant on warm sunny days in the spring forest. Insect pollinators feed intensively with deliberate flights between flowers. Individual insects remain faithful to specific flowers for extended times on their foraging bouts, but occasionally sample nectar from other flowers. A bee working a patch of spring beauty will likely skip over dozens of violets, , and trout lilies just to find the next spring beauty. Different flower are easily recognized by color, nectar guides, shape, and odor to provide insects with the means for quick identification on their forays. Migrating hummingbirds also participate in the act of on the hanging red flowers of columbine (Aquilegia canadensis) that colonizes light gaps within the forest. Many spring ephemeral flowers are designed for cross-pollination. Physical separation of anthers and stigmas is commonly employed as a means to reduce self-pollination in hermaphroditic (i.e., flowers with both that produce pollen and ovaries that produce producing) flowers. Some woodland herbs utilize a chemical interaction between pollen and stigmas to inhibit “self-pollen” from germinating on styles of the same plant (i.e., self incompatible pollen). Wild sarsaparilla (Aralia nudicaulis), white trillium (), trout lily and bunchberry ( canadensis) are a few woodland herbs with a self-incompatibility mechanism. An out-crossing breeding system shuffles and maintains genetic variation within populations of a species. Genetic variation can manifest itself in subtle differences in characteristics such as flower color, nectar guides, pubescence and size and shape in many woodland flowers. Flowers on the same plant should be nearly identical and but differences likely exist on flowers of neighboring of the same species. A careful observer in the forest can easily see distinct differences in flowers of trillium, spring beauty, and liverleaf within a population. Much of this floral variation has a genetic basis just as hair and eye color on humans. Like humans, maintenance of variation in the population is due to a mating system where sexual encounters between different individuals of the same species are the norm. 2

Self-pollination and self-compatibility have evolved in a few woodland herbs. This means of sexual reproduction minimizes genetic variation, but guarantees reproductive success when numbers are low. Spotted touch-me-not (Impatiens capensis) grows along streams and moist areas of the forest. The large flowers of this handsome plant are designed for cross-pollination (chasmogamous flowers), but individual plants also produce closed flowers lower on the plant body. These cleistogamous flowers promote self-pollination by forcing anthers to contact the in the closed flower . Many species of violets have chasmogamous and cleistogamous flowers similar to spotted touch-me-not. Insects also learn to discriminate between closely related flowers (Figure Reproductive Isolation). At least a dozen species of violet live in eastern forests. A few species are reproductively isolated by flowering very early like round- violet ( rotundifolia) or by flowering very late like purple forest violet (Viola adjunca). For those species that flower simultaneously and in close proximity to one another, the challenge is to attract faithful bumble bees to encourage pollen movement only between flowers of the same species. Forest violets rarely hybridize, and any pollen movement between violet species will result in the waste of pollen and perhaps lower reproduction. The pale violet (Viola striata) produces cream- colored flowers with violet nectar guides and a short nectar spur. The long-spurred violet (Viola rostrata) has violet colored flowers with dark blue blotches towards the inside of and a very long nectar spur. Canada violet (Viola canadensis) has pure white flowers with purple lines and a yellow center. The downy yellow violet (Viola pubescens) produce bright yellow flowers with reddish nectar guides. All bloom profusely along our trails and maintain a high degree of pollinator fidelity, and maintain their unique species identity. Bumble bees foraging in a mixed violet population use the differences in visual, tactile, and olfactory cues to move between flowers of the same species. As long as the foraging bout remains profitable, bumbles will stick to flowers of the same species and change flowers only when nectar rewards decline below some threshold. Floral traits can also serve as guideposts or reminders of caloric rewards when a bumble flies to new patches of flowers much like the golden arches have become icons for high calorie hamburgers when visiting a new town. Dutchman’s breeches (Dicentra cucullaria) and squirrel corn (Dicentra canadensis) provide another story of pollination and insect discrimination. Native bumble bees pollinate both species. Pollination mistakes are seldom made and even if cross-pollination between the species results, would not be produced. Squirrel corn flowers are fragrant and the petals have rounded bases. Dutchman’s breeches have sharply-angled petal bases and no odor. These powerful recognition signals allow discriminating bumble bees to concentrate on one species of flower at any given time. Not all spring ephemerals value insect pollination (Figure Wind Pollinated Forest Herbs). The forest sedges (Carex) and early meadow rue (Thalictrum dioicum) produce less conspicuous flowers and larger and more numerous stamens higher off the ground than insect-pollinated flowers. Anthers 3 of these two plants rock back and forth in gentle spring breezes broadcasting pollen to the surrounding forest floor. Large feathery stigmas capture pollen on the wind. Much of the pollen is lost to the forest floor which is why these plants must produce many stamens, large anthers, and more pollen. Even though evolution has lead to a waste of pollen grains, these species are less exuberant in their advertisement and save energy by not attracting and rewarding insects with colorful, energetically costly nectar-bearing flowers. The lack of color in the flowers may also prevent insects from being attracted and then stealing pollen. Natural selection has acted along different paths to meet the same requirements for reproduction. Flowering does continue in the herbaceous zone of forests well into June and July, although less profusely. The early, colorful flowers are gradually replaced with those of white (Figure Summer Woodland Flowers). In the darkened forest, white stands out more strongly against green leaves on the forest floor rather than red or pink. Forest bees and flies continue to pollinate that late flowering species such as foam flower (Tiarella canadensis), Canada mayflower (Maianthemum canadensis), bunchberry, starflower (Trientalis borealis), teaberry (Gaultheria procumbens), false solomon’s seal (Smilicina racemosa), baneberry (Actaea alba), wild sarsaparilla, and partridgeberry (Mitchella repens). The pollination system of partridgeberry is unique among the forest herbs (Figure Partridgeberry Flowers). Individual plants produce one of two flower types and both flowers have tubular corolla with pubescent petals. The “pin” type flower has a four-pronged stigma that unfolds beyond the open petals. The four anthers are located on top of shortened stamens within the corolla tube in pin flowers. The “thrum” type flower has the reverse morphology. The four-lobed stigma opens within the corolla tube and the stamens protrude beyond the petals to expose the anthers. Legitimate pollination occurs in specific directions: thrum pollen to pin stigmas and pin pollen to thrum stigmas. The physical separation of stigmas and anthers ensures that pollen deposition and retrieval on insects occurs on different regions of their body for the appropriate pollination pathway. When mistakes are made, the plant has a built-in biochemical pollen recognition system to reject pollen from illegitimate . The redundant pollination system guarantees that reproduction occurs only between unique compatible individuals. Reproduction for any organism requires a tremendous energy investment. Forest perennials attempt to maximize leaf surface area on flowering stems in order to maximize and increase food production. Bunchberry has six leaves on flowering stems as compared to four on non-flowering ones. Canada mayflower and trout lily both produce two leaves on flowering stems as compared to one on non-flowering stems. This pattern is repeated on other forest herbs. The energy investment is not partitioned equally between sexes. Sperm, packaged in pollen, is relatively inexpensive to produce. Pollen is abundant, cheap, and more expendable. 4

The strategy is to make a plethora of sperm and hope to sire seeds on many different plants. Female reproduction in terms of eggs, seeds, and fruits is outrageously expensive. Seeds contain developing and tissues rich in lipids and carbohydrates to provide the neophyte with energy to start life. Fruits package seeds into a dispersal vehicle surrounded with attractive pigments and energetic rewards to employ animals to carry away the fruit. Other fruits engineer plumes for wind dispersal, and some have catapults and springs to cast the seeds away. Jack-in-the-pulpit has evolved a cleaver strategy for partitioning sexual roles among plants depending on levels of stored resources (Figure Jack-in-the-pulpit Sexual Operations). Small dipterans (flies and gnats) visit the jack-in-the-pulpit . Teasing away the spathe or leaf-like pulpit reveals a small battery of flowers below the elongated club- shaped spadix. These inflorescences bear either staminate or pistillate flowers, but never both. Staminate inflorescences are borne on plants with a single, three-parted leaf. The male plant is noticeably smaller than plants bearing pistillate inflorescences and two giant leaves. Jack-in-the-pulpit determines its reproductive strategy by measuring its stored resources in the underground corm. Successfully pollinated pistillate flowers will ripen large red berries that are eaten and dispersed by and small mammals. Perhaps a better name for the larger and more robust plants of this species might be “Jill-in-the-pulpit.” As successive seasons of seed and fruit production depletes a plant’s energy budget, a female plant may return to male-hood until sufficient resource levels are acquired once again. Herbaceous perennials rarely record their age and history as clearly and precisely as trees in the temperate zone. Observers are left to their own imagination and speculation on the age of these plants. However, some species with clonal growth allow ages to be estimated. If a clone of wild ginger (Asarum candense) has an 2.5 meter radius and stems grow outward at a rate of four inches per year, then the plant should be in the neighborhood of 25 years old (250 cm / 10 cm per year). Such an analysis may work for species with a clonal growth pattern such as bluebead (Clintonia borealis) and wild ginger, but it is impossible to estimate age when clones interdigitate or the connection between sections of the clone degrade with time. In these situations, a genetic fingerprint in the laboratory or matching floral morphology may provide insights into the clonal structure of a population. Trillium and American ginseng (Panax quinquefolium) record their history and age in a series of leaf scars that encircle the (Figure Trillium Age Series). Mature trilliums produce a single stem with three leaves and a solitary flower. As the stem senesces, a scar is made on the underground giving it a bumpy appearance. Stem scars are preserved along the length of the rhizome, although older sections of the rhizome may eventually be self-pruned. Careful excavation of a trillium rhizome reveals that many plants are older than 30 years of age! This is really a surprise to most forest goers who don’t see age reflected in the beauty and/or color of the trillium flowers. 5

It is equally surprising to discover how old trillium plants are when they first flower. Trillium seeds may germinate two springs after dispersal. One year old plants produce a single spindle-shaped leaf upon a rhizome the size of a small bead. Over the next few years, the juvenile trillium plant produces larger leaves that become more heart-shaped. The three-leaved juvenile plant forms between years 6 and 10. Trillium plants may flower for the first time between 10 and 15 years of age. Trillium plants ride the edge of their energy budget. Leaf damage by storms, heavy browsing by unnaturally high populations of deer, or thoughtless flower and leaf gathering by people may bring death to the plant. For those who feel the need to collect trillium flowers, respect the fact that you may be sacrificing an elder reproducing member of the forest community in exchange for a few days of interior decorating. Bunchberry is a forest herb with an of small flowers encircled by four showy . The inflorescence and floral structure is similar in design to its cousin, flowering dogwood (Cornus ). Bunchberry is common in boreal forests and bog communities. It flowers in early summer, is self-incompatible, and produces red berries in the fall with single seeds. Buncherry flowers explosively open when triggered by heavy insects. The explosion is energized by that has built up in elongating cells of petals and stamens. Anthers are held together and stamens bend outward while in bud. Within 0.5 milliseconds of the flower opening stored elastic energy in the filament rotates the anther heads upward in a trebuchet-style launch to reach a maximum vertical velocity of 7.5 meters per second (see videos at http://www.nature.com/nature/journal/v435/n7039/suppinfo/435164a.html). As the anthers reach their terminal velocity, pollen is launched upward from the flower. Pollen launching embeds pollen in bristles of the insect that triggered the flower opening. This ballistic mechanism of attaching pollen improves the chance that insects will transport pollen to the stigmas of other bunchberry flowers. Flower opening and the ballistic launch of pollen may also happen in the absence of insect visitors to bunchberry flowers. Whittaker et al. (2007) propose that self-launching allows for wind pollination in dense populations when insect pollinators are absent. Fruit and seed production from inflorescences where insects were excluded from visitation supports their hypothesis that wind-pollination may be effective in the deciduous forest. Consider for a moment that most of was recovering from a glacial period 12,000 years ago. The North American temperate forests were expanding their ranges northward from refugia along the Gulf and Atlantic coastal plains in the southeastern and southern . The trees and herbs recolonized eastern North America by seed dispersing birds, mammals, and wind. Or did they? Palynological studies (see chapter on bog forests) suggests that trees raced northward across North American at rates of 300-500 meters per year (Footnote: The word “raced” is relative to the observation that we don’t see plants move. When the climate changed over 15,000 years at the end of the last ice age, movement was a race. Today, ecologists are concerned that forests will be unable to keep up with a changing climate due to anthropogenic global warming.). We might assume the same for the forest herbs. Assume that a forest herb resided in the southern Appalachian Mountains in northern 15,000 years ago, but that same species now occurs in southern Canada near Montreal. This species dispersed nearly 1600 linear kilometers in 15,000 years (106 meters per year). Is it possible for herbaceous seeds to be transported slightly more than a football length every year for 15 millennia? 6

Today, many of our forest herbs appear to be adapted for dispersal (i.e., ; Figure Ant Dispersed Seeds). How could a fruit or seed be adapted to ? These invertebrates are very common on the forest floor and are active in early summer when seeds are ripening. Trillium, bloodroot, violets, and trout lily fruits drop or lay their fruits on the ground where ants can harvest the seeds. The seeds of these plants possess an accessory (i.e., eliaosome) that is rich in fatty acids that attract ants. Seeds are collect by ants and transported underground where the eliasome is removed and used for food. The seed is then discarded into an organic rich refuse area of the ant nest. This provides the seed with a luxury seed nursery to begin their life. Kalisz and colleagues (1999) examined the dispersal of hundreds of radioactively labeled white-flowered trillium seeds in a deciduous forest. They determined that ants were effective dispersers of trillium seeds, albeit over short distances. In one year of the study mean dispersal distance was 2.5 meters, but only 0.5 meters in the following year. This is a far cry from the necessary dispersal of 106 meters per year to reach southern Canada from Georgia! Whether ants are responsible for the post-glacial recovery of forest herbs remains an important question. Zettler and colleagues (2001) observed that yellow jacket wasps can disperse some southeastern trillium greater distances than ants. Recent studies by Myers and colleagues (2004) suggest that plants like trillium may have hitched rides within the gut of deer. Recovery of deer pellet yield trillium seeds that remained viable and germinated in trials. Given the long retention time of trillium seeds within the gut and the mobility of deer, is easily accomplished over hundreds of meters and occasionally as great as 3 kilometers. These data suggest that some ant-mediated plants receive helpful dispersal from mammals. Painted trillium (Trillium undulatum) is locally abundant in the southern Appalachians and northeastern North America. Unlike the other common trilliums, this species has been shown to produce seed that is genetically identical to the maternal plant and therefore not a direct product of pollination. Even though pollination is unnecessary, this species has large white flowers with red chevrons toward the base of the petals. Painted trillium seeds possess eliasomes, but the fruit matures to a bright red and may attract mammals and birds as a primary disperser. Seeds dropped by the primary frugivore can then be further disseminated to nursery sites by ants. Thus, painted trillium may enjoy the luxury of having co-dispersers. Ballistic self-dispersal of seeds and fruits occurs in geranium, spotted touch-me-not, and violets. In the case of geranium, ballistic dispersal is the sole mechanisms of seed movement and the mechanism is capable of throwing seeds 9m from the maternal plant. Violets may throw their seeds in preparation for secondary dispersal by ants to more distant locations in the population. The initial dispersal event may reduce the risk of seed close to the maternal plant in violets. Ballistic seed dispersal in spotted touch-me-not may also improve the chance of secondary dispersal. Touch-me-not lives in moist water-logged soils and with floating seeds water may serve as the secondary dispersal agent. 7

Many herbaceous perennial fruits have brightly colored fruits (Figure Fruit Flags) and attract birds and mammals as dispersers. At least one scientific report suggests box turtles can serve as potential dispersers. There are many red-colored fruits such as red baneberry, partridgeberry, Canada mayflower, jack-in-the-pulpit, and false Solomon seal. Several purple or bright blue fruits can be found on blue bead, blue cohosh, and Indian cucumber. Several plants advertise their fruits by contrasting fruit color with showy leaves or pedicels. Doll’s eye’s (Actaea alba) bright white fruits with black spots contrast nicely with bright red pedicels and the purple fruits of Indian cucumber contrast with an upper of three leaves that turn red in the fall. The woodland alternate-leaved dogwood displays its bluish fruits on red pedicels. Fall is not without its own show of flower color , provided by several woodland goldenrods, asters and lettuces, all members of the Composite or Sunflower . Like their cousins in fields and roadsides, the woodland asters have showy inflorescences and a generalist pollination system. and beetles are frequently seen on these flowers especially in light gaps and forest edges where the floral displays are most intense. References: Cain, M.L., B. G. Milligan, A.E. Strand. 2000. Long-distance seed dispersal in plant populations. American Journal of 87:1217-1227. Beattie, A.J. and N. Lyons. 1975. Seed dispersal in Viola (Violaceae): Adaptations and Strategies. American Journal of Botany 62:714-722. Handel, S.N. and A.J. Beattie. 1990. Seed dispersal by ants. Scientific American. Braun, J.; Brooks, G. R. 1987. Box turtles (Terrapene carolina) as potential agents for seed dispersal American Midland Naturalist 117: 312-8. Kalisz, S., F. M. Hanzawa, S. J. Tonsor, D. A. Thiede, and S. Voigt. Ant-mediated seed dispersal alters pattern of relatedness in a population of Trillium grandiflorum. Ecology 80:2620-2634. Myers, J.A., M. Vellend, S. Gardescu, and P.L. Marks. 2004. Seed dispersal by white-tailed deer: implications for long-distance dispersal and migration of plants in eastern North America. Oecologia 139: 35-44. Whigham, D. F. 2004. Ecology of woodland herbs in temperate deciduous forests. Annual Review of Ecology, Evolution and Systematics 35:583-621. Whitaker, D.L., L.A. Webster, and J. Edwards. 2007. The biomechanics of Cornus canadensis stamens are ideal for catapulting pollen vertically. 21:219-225. 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.