The Lady Slipper newsletter, and now blog, of the Kentucky Native Plant Society has been published since the Society’s founding in 1986. We occasionally feature an article from a past issue. In this article from 2007, Amy McIntosh discusses members of the Birthwort Family, Aristolochiaceae . This article ran in Vol. 22, No. 2. If you would like to see these and other past issues, visit the Lady Slipper Archives, where all issues from Vol. 1, February 1986 to Vol. 40, 2025, can be found.
Aristolochiaceae: Insects, Humans and the Birthwort Family
by Amy McIntosh
Introduction
Members of the Birthwort Family, Aristolochiaceae, have a complex array of relationships with insects and humans. Interactions with pollinators, non-pollinating butterflies, and seed/fruit dispersers (along with the plants’ pollination mechanisms and the creation and use aromatic oils) provide insight into the family’s co-evolution with insects.
Human relationships with the birthwort family have a long history involving herbal and food use. Current interests in the family include collection of garden and greenhouse specimens, breeding of ornamental varieties and determining effectiveness of possible anticancer chemicals within some species. Human degradation of habitat in areas of endemic and otherwise limited populations has threatened 35 species at last count.
Attracting Pollinators
Unlike some flowering plants that boast a bright, colorful perianth, most Aristolochiaceae members possess green, brown, black, deep purple or pale yellow calices (Huber 1993). Some members of the family utilize self-pollination as the major means of sexual reproduction (e.g., Asarum europaeum European wild ginger) (Huber 1993). Aristolochia serpentaria (Virginia snakeroot) is suspected to exhibit cleistogamy (propagation by means of closed, self-pollinating flowers) (Pfeifer 1966). Others have flower maturation that restricts self-pollination temporally (for example, Aristolochia maxima (Florida dutchman’s pipe) is protogynous (explained below)) (Sakai 2001).
Species of Aristolochiaceae which are dependant on pollinators attract true flies (Diptera), beetles (Coleoptera) and thrips (Thysanoptera) with odor and floral food rewards (Sakai 2001). Warmth is an attractant as well (Thein et al. 2000). The lack of colorful flowers and the presence of floral odors suggest the early evolution of the family among angiosperms (Pellmyr and Thien 1986).
Floral odors
Aristolochiaceae flowers generally emit strong, fetid floral odors mimicking musky fruit, fungus, urine, feces or carrion (Huber 1993; Sakai 2001; Cronquist 1981). In some carrion-scented flowers it is suggested that this scent is evidence of an adaptation to attract unsuspecting pollinators that originally fed and oviposited on carrion but now utilize floral tissues (Pellmyr and Thein 1986). Aristolochia grandiflora (pelicanflower, an exotic growing in Florida) was noted (on a label of a herbarium specimen deposited at the New York Botanical Gardens) as having a “strong odor of putrid meat [that] attracts the insects 100 or more feet from the flower” (Reis and Lipp 1982). The odors produced by early angiosperms (such as Aristolochiaceae) may even trigger insect mating (Pellmyr and Thein 1986).
Thermogenesis
Aristolochiaceae flowers produce heat through biochemical processes (called thermogenesis). Maximum heat production is synchronized with the stigma(s) ability to receive pollen. This production of heat is theorized to benefit basal angiosperms in many ways including enhancing floral odor release and pollen germination. The warmth also benefits pollinators by conserving the insects’ energy and providing a good environment for breeding and development of larvae (Thein et al. 2000).
Flower rewards
Floral tissues are rich in energy and provide a competitive edge for ovipositing female insects and resulting larvae (Pellmyr and Thein 1986). Hexastylis is pollinated by thrips (Thysanoptera), which eat pollen grains and flower epidermal tissue. Thrips spend most of their life cycle within the flowers (USFW, 1990), (Sakai 2001). Two species of Aristolochia flowers (A. maxima and A. inflata) are known to provide ovipositing substrate for pollinators. The pollinators of these two flowers are predominantly female, indicating a coevolved link between the reproduction of the insects and plants (Sakai 2001).
Diptera (true flies) have specialized mouthparts that allow the imbibing of sweet floral liquids that are found on basal angiosperms’ stigmas, ovaries and stamens (Thein, et al. 2000). Although flies of several families are known to pollinate Aristolochia, the attraction is usually deceptive, and nectar and similar liquids may or may not serve as a reward depending on the plant species. These liquids may serve an alternative role in attraction, feeding the pollinator only during entrapment, or simply in attaching pollen grains to the insects’ bodies (Sakai 2001).
Pollination Mechanisms
In addition to these means of attracting pollinators, many Aristolochiaceae flowers are equipped with mechanisms that assist in insect pollination: floral traps and protogynous floral maturation. Floral trapping techniques allow for entrance and retention of a potential pollinator until the flower has been pollinated. This is accomplished by utilization of stiff directional hairs in the perianth tube leading to the utricle and/or an oily covering on epidermal cells which prevents traction (Huber 1993). Such trapping utricles limit competition for flower rewards and provide a safe haven for mating insects (Pellmyr and Thein 1986).
Protogynous flowers (observed in Aristolochia species) have “female” and “male” stages (days). On the first (female) day, the flowers may emit an odor to attract pollinators. The female organs are mature and prominent; stigmas are able to accept pollen and heat is produced inside the utricle. On the second (male) day the anthers become prominent and dehisce, covering the trapped insect with pollen. Subsequently perianth tube hairs wither and allow for the insect’s movement to another female-day flower in need of pollination (Pfeifer 1966; Hickey and King 1998).
Food Plant use by Papilionidae
Several genera of Papilionidae (swallowtail) butterflies utilize Aristolochiaceae for food plants. In fact, entire swallowtail tribes (Serynthiini and Troidini) are host specific to Aristolochiaceae. Caterpillars that feed on Aristolochiaceae plants are able to utilize aristolochic acids as predator deterrent (Tree of Life 2004).
In North America Battus (pipevine swallowtails) predate on Aristolochia species. Several genera of the Papililionidae are parasites on Asian Aristolochiaceae species. Archion and Zerynthia are distributed in the western palaearctis with their host plants. Bragantieae and some Aristolochia are eaten by Troides species (Huber 1993).
The swallowtail butterfly has two broods a year; the larvae consumes all of the foliage of the plant on which it emerges and seeks additional host plant individuals. Such ravenous feeding by the larvae results in lower plant reproduction success. These selective forces, over time, have resulted in adaptations by some species to prevent herbivory: tough leaves low in nutritional value and taste; high root-shoot ratios to store food for high predation years; and underground flower and fruit production (which are preferred to foliage by the insects) (Rausher and Feeny 1980).
Seed/Fruit dispersal
Aristolochiaceae utilizes a variety of fruit and seed dispersal mechanisms. Like many other temperate woodland herbs, ant-plant mutualism (called myrmecochory) plays an important role in the distribution of herbaceous species’ seeds (notably Asarum and Hexastylis). Aristolochia is dispersed by wind after fruits dehisce. Sticky seeds, edible fruit and water dispersal are alternative means of dispersal utilized by the family.
Hexastylis seeds have copious eliasomes (fat bodies) which are readily eaten by ants. In fact, Gaddy (1986) noted consistent 100% removal rates of Hexastylis seeds by ants in experiments where a wide range of seed types were made available. This rich food source results in hoarding of the seeds at ant nest sites, where germination in clusters occurs the following spring (USFW, 1990). Similar observations have been made of Asarum europaeum seeds, which are dispersed by Formica polyctena (Gorb and Gorb 2003).
Asarum (wild ginger) seed are prone to desiccation (Kelly 1998). This coupled with dispersal limitations of myrmecochory may play a role in limited range of Asarum (in comparison to Aristolochia).
Many Aristolochia species have winged seeds that are dispersed when the fruits dehisce (Huber 1993). Some additional groups are distributed by animals: Aristolochia by means of sticky seeds that attach to animal bodies and Paristolochia by encouraging consumption of fragrant, edible fruits (Huber 1993). Aristolochia clematitis (birthwort) and two Amazonian species of the family possess fruits and seeds that are adapted for distribution by water (by means of floating) (Wulff 1943; Huber 1993). Aristolochia’s variety of dispersal techniques which favor a longer-distance results can help to explain the group’s wide distribution, including colonization of many isolated islands in Central America and Asia.
Human History of Medicinal Use
Members of the Aristolochiaceae have a long history of medicinal use, as evidenced by the inclusion of Aristolochia clematitis in medieval woodcut-illustrated herbals and commonly in later engravings. In fact, the name Aristolochia has roots in the Greek: Aristos (meaning best) and lochia (meaning delivery/birth) (Pfeifer 1966). Pliny referenced the use of Aristolochia by midwives, and termed it aristi lekhousais (translated—best for women giving birth) (Coffey 1993). The common name of Aristolochia clematitis further recognizes this common use of the “herb”. In addition, in keeping with the Doctrine of Signatures, the flower bud of members of Aristolochia was determined to resemble the human fetus or swollen womb and was utilized accordingly to remedy the pain of childbirth (Pfeifer 1966), and as an abortive agent, conception aid (and, ironically, preventative), and birth inducer (Coffey 1993).
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Aristolochiaceae members have been determined in the past to possess many additional medicinal benefits. The family’s widespread use for a myriad of ailments is indicated by the use of its name by an honorary society of herbalists in the United States—The Aristolochite Society (now known as Rho Chi) (Pfeifer 1966). Aristolochia serpentaria (of North America) was prized as an antidote for snakebite, with records of this fact dating as early as 1633 (Coffey 1993). A. schippi (Honduras) and A. trilobata (Martinique) were used similarly for snakebikes, and Aristolochia bracteolata (of Tropical East Africa) for snakebite and scorpion stings (Reis and Lipp 1982; Verdcourt 1986). In keeping with a strong Chinese awareness of potential uses of herbs, Chapman and Wang (2002) list Aristolochia debilis as possessing antirheumatic, and diuretic properties. Other historical uses of the Asarum and Aristolochia include to cure ulcers, syphilis, rheumatism, cholera, relieve toothache, fever, indigestion, coughs, heart conditions, throat ailments, cramps, gas and to promote sweating (Foster 2000; Coffey 1993)
Recent research has shown that medicinal usefulness of the plants is not unfounded. Asarum’s rhizomes contain essential oils (sesquiterpenes and phenlypronanoid compounds), and aristolochic acid from aporphines is found in Tribe Bragantieae and Tribe Aristolochieae members (Huber 1993). These agents are currently being researched for anti-cancer and antibiotic properties, although the family also bears a reputation of possessing poisonous and carcinogenic properties (Foster 2000; Coffey 1993; Polunin 1969).
Non-medicinal Uses
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Aristolochiaceae members have been utilized for a variety of non-medicinal applications. Fruits, leaves, rhizomes and stems of the Aristolochia debilis were suggested in a circa 1406 AD list (the Chiu Huang Pen Tsao) as famine foods (Chapmand and Wang 2002). Aristolochia bracteolata (Africa) is reportedly used for food as well (Verdcourt 1986). Wild ginger (Asarum canadense of North America) has been known as a substitute for true tropical ginger (Zingiber spp.) (Coffey 1993). Pararistolochia (Aristolochia) triactina is used as a rope for various applications including binding hut materials in its native Uganda, Angola and nearby countries (Verdcourt 1986). A. daemoniana shares a similar use in British Guiana (Reis and Lipp 1982).
The unusual flower shape in many Aristolochia species have made them prized for ornamental use. Aristolochia gigantea (Brazilian dutchman’s pipe) and A. littoralis (calico flower) are common greenhouse tropicals and A. macrophylla (Dutchman’s pipe) is grown in many temperate gardens of the world (Pfeifer 1966). Aristolochia and Asarum species have been manipulated through hybridization to produce large, showy and unusual forms for collector-gardeners in many parts of the world.
Aristolochiaceae in Kentucky
Kentucky boasts eight species of the birthwort family, including representatives of three genera. Dutchman’s pipe (Aristolochia macrophylla) is a woody vine of mixed mesophytic forests and can be found growing to diameters exceeding 2 1/2”. Pipe-vine (A. tomentosa), is also a lianas, but inhabits swamps and wet woods of the Mississippi embayment.
Virginia snakeroot (A. serpentaria), a herb, completes the state’s constituents of the Aristolochia genus. Wild ginger, Asarum canadense, is common in moist woods throughout Kentucky and varies in floral color from greenish to deep burgundy with a wide range of sepal length.
In Kentucky the heartleaf and little brown jugs (genus Hexastylis) are restricted to the Appalachian region. One species, H. arifolia is relatively common, but the other three species, H. virginica, H. contracta, and H. heterophylla, are all rare and state-listed (Jones 2005).
Outlook for Aristolochiaceae
According to the World Conservation Monitoring Centre (1997), 35 Aristolochiaceae species are included on “red list” of threatened plants. These include four species and one variety found in the southeast of the United States: Hexastylis contracta (KY, NC,TN), H. naniflora (NC, SC), H. rhomiformis (NC), H. speciosa (AL), and H. shuttleworthii var. harperi (AL, GA).
Although some species of the family have been heavily harvested in the past for medicinal use (Coffey 1993), this threat has mostly subsided. High endemism (including some island endemism) and small ranges for many species make even minimal habitat destruction have an enormous impact.
Continued habitat degradation for agriculture and timber harvesting in tropical region impose a significant threat to much of the Aristolochieae tribe. Other potential concerns are present for species highly coevolved with pollinators and seed dispersers if insect populations are reduced.
Literature Cited
Chapman, G. P. and Y. Z. Wang. 2002. The plant life of China: Diversity and Distribution. Springer-Verlag, New York. 256 pp.
Coffey, T. 1993. The history and folklore of North American wildflowers. Facts on File, Inc. New York. 356 pp.
Cronquist, A. 1981. An integrated system of classification of flowering plants. Columbia University, New York. 1262 pp.
Foster, S. and J. A. Duke. 2000. A field guide to medicinal plants and herbs of eastern and central North America. 2nd edition. Houghton Mifflin Company, New York. 411 pp.
Gaddy, L. L. 1986. Twelve new ant dispersed species from the southern Appalachians. Bulletin of the Torrey Botanical Club. 113:3:247-251.
Gorb, E. and Gorb, S. 2003. Seed dispersal by ants in a deciduous forest ecosystem: mechanisms, strategies, adaptations. Kluwer Academic Publishers; Boston, Massachusetts. 225 pp.
Hickey M. and C. King. 1988. 100 families of flowering plants, 2nd ed. Cambridge University Press, Cambridge. 619 pp.
Huber, H. 1993. Aristolochiaceae. Pages 129-137 in Kubitzki, K., ed. The families and genera of vascular plants. Volume 2: Flowering Plants—Dicotyledons—Magnoliid, Hamamelid and Caryophyllid Families. Springer-Verlag, New York.
Jones, R. L. 2005. Plant life of Kentucky. University of Kentucky Press: Lexington, Kentucky. 834 pp.
Kelly, L. M. 1998. Phylogenetic relationships in Asarum (Aristolochiaceae) based on morphology and ITS sequences. American Journal of Botany. 85(10)454-1467.
Pellmyr O. and L. B. Thien. 1986. Insect reproduction and floral fragrances: key to the evolution of angiosperms? Taxon 35:76-85.
Pfeifer, H. W. 1966. Revision of the north and central American hexandrous species of Aristolochia (Aristolochiaceae). Annals of the Missouri Botanical Garden. 5:2:115-196.
Polunin, O. 1969. Flowers of Europe. Oxford University Press, London. 662 pp.
Rausher, M. D. and Feeny, P. 1980. Herbivory, plant density, and plant reproductive success: the effect of Battus Philenor on Aristolochia Reticulata. Ecology. 61(4): 905- 917.
Reis, S. V. and F. J. Lipp, Jr. 1982. New plant sources for drugs and foods from the New York Botanical Garden Herbarium. Harvard University Press: Cambridge, Massachusetts. 363 pp.
Sakai, S. 2001. Aristolochia spp. (Aristolochiaceae) pollinated by flies breeding on decomposing flowers in Panama. American Journal of Botany. 89(3)527-534.
Thien, L. B. et al. 2000. New perspectives on the pollination biology of basal angiosperms. International Journal of Plant Sciences. 161(6 suppl.)225-235.
Tree of Life web project. http://tolweb.org/tree/ phylogeny.html. Accessed 12/06/04.
U. S. Fish and Wildlife Service Division of Endangered Species. Dwarf-Flowered Heartleaf (Hexastylis naniflora). Endangered and Threatened Species of the Southeastern United States (The Red Book). FWS Region 4. http:// endangered.fws.gov/i/q/saq5g.html. Accessed 11/23/ 2004.
Verdcourt, B. 1986. Aristolochiaceae. Flora of Tropical East Africa series. Royal Botanic Gardens, Kew. 11 pp.
World Coservation Monitoring Centre. 1997 IUCN Red List of Threatened plants. http://www.wcmc.org.uk. Accessed 11/28/04