Geography 316:  Biogeography     In progress 12/12/2003

The Biogeography of  Sweet Fennel (Foeniculum vulgare) in California .
by Christina J. Horrisberger, student in Geography 316  Fall 2003

Thank you for visiting our site. This web page was written by a student in Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD.  All photos and maps are posted with specific copyright permission for the express use of education on these web pages. The students have tried to be as accurate as possible with the information provided and sources and references are cited at the end of each page.

Noxious weed:  any species of plant that is, or is liable to be, troublesome, aggressive, intrusive, detrimental, or destructive to agriculture, silviculture, or important native species and is difficult to eradicate. (California Food and Agricultural Code)

 

Kingdom               Plantae Subkingdom         Tracheobionta Superdivision        Spermatophyta         Division                Magnoliophyta  Class                     Magnoliopsida Subclass                Asteraceae Order                    Apiales Family                   Apiaceae Genus                    Foeniculum P. Mill. Species                  Foeniculum vulgare P. Mill. Common Name     sweet fennel

© John M. Randall/The Nature Conservancy

 Description and Natural History

Although the Apiaceaes (formerly Umbelliferae) or carrot, family comprise one of the largest assemblages of herbaceous plants, Foeniculum vulgare P. Mill., commonly known as fennel, is the only known species of the genus Foeniculum. While there are several cultivars of fennel that are currently cultivated as a food crop, the cultivar considered here- sweet fennel, is considered a noxious weed in several regions in the western hemisphere and can be observed in disturbed coastal areas throughout central and southern California. Foeniculum vulgare is prolific where present and often forms large, dense stands that are noticeable even from a distance. It is an upright, perennial, herb that grows to heights ranging from 3.3 to 12 feet tall (Klinger 2000), and is distinguishable by the strong anise like scent that originates from its foliage and seeds. Finely dissected, pinnate leaves that range from 4-24 inches in length sheath the solid, erect stems originating from a central crown that is similar to its close relative celery (Bean and Russo 1988). Compound umbels composed of tiny yellow flowers that radiate out from a central point atop the stems make this plant attractive to insects. As is characteristic of many Apiaceaes, Foeniculum vulgare acquires nutrients through a long taproot and ovate, ribbed seeds high in aromatic essential oils are produced after flowering. The growth period for Foeniculum vulgare ranges from late winter to late fall and flowering begins in early spring, with the main blooming period between May and September (Bean and Russo 1988).

Foeniculum vulgare has been cultivated and used by humans for centuries and like many members of the Apiaceae family it is a popular herb and spice. It has a strong aroma that is very similar to anise or licorice and has long been a popular food source in many cultures. Although all parts of the plant are edible, sweet fennel is not currently commercially cultivated, because unlike its cultivated relatives, sweet fennel does not form the bulb-like base that is a popular vegetable. Where naturalized or cultivated in the small garden, however, the leaves are used as an herb or garnish, the seeds make a useful spice, and the young stems are eaten both raw and cooked. Additionally, parts of the plant may be chewed or a tea can be made from the fronds and seeds to aid in digestion and relieve gastrointestinal discomfort. In southern Europe where Foeniculum vulgare is native, the leaves were used ceremonially by the Romans to create celebration garlands for warriors. Similarly, after introduction into California, the fronds were spread on floors of Spanish missions to release their sweet scent to the congregations (De Ruff 1999). ). Furthermore, many organic gardeners now cultivate Foeniculum vulgare for use as an herb and especially to attract beneficial insects including ladybird beetles, wasps, butterflies and butterfly larva, and lacewings to the garden. Although it can be a desirable food source and garden plant, Foeniculum vulgare is highly invasive and efforts must be made to contain the spread of the plant. Throughout the state of California measures are currently underway to eradicate sweet fennel from areas where it grows in the wild. 

Evolution

Foeniculum vulgare is the only species in the genus Foeniculum, which is one of approximately 300 genera in the Apiaceae (carrot) family. Apiaceae is the largest of three families that comprise the order of flowering plants called Apiales and the two smaller families are Araliaceae (ginseng) and Pittosporaceae. Apiaceae and Araliaceae are the closest relatives and both are characterized by their wide distribution, ability to self-pollinate or be pollinated by a variety of organisms and by their distinctive umbrella-like arrangement of tiny flowers called umbels (Introduction to Apiales 2003). The flowers are usually white or yellow and their group arrangement is an evolutionary trait developed to attract pollinators. Another evolutionary trait developed by many Apiaceae is the production of ethereal oils that repel predators (MOBOT 2003). It is the presence of these aromatic oils that make them popular herbs and spices for humans and their swollen roots make many Apiaceae an important food source. Most Apiaceae are herbaceous and many, including celery, carrots, dill, cumin, parsley and anise, in addition to Foeniculum vulgare (fennel) are economically valuable. It is also true, however, that some are highly toxic, such as the poison hemlock that poisoned Socrates.

Pollen records for Apiales can be traced back as far as the Cretaceous and records of Eocene fossil pollen for Apiaceae have also been identified. Because of their longevity, wide distribution and anthropogenic history, Apiaceae were one of the first plant groups to be systematically classified in the end of the 16^th century, however, taxonomy of the time was based largely on morphology and it is only now that Apiales are being reclassified according to their genetic traits. Until recently Apiales were constituents of the subclass of Magnoliopsida titled Rosidae, but as scientific knowledge has progressed it has become evident that the genetic make-up of Apiales falls more closely into the subclass Asteracaes and further that they are part of the Eurasterids II clade (Asterids 2003). As knowledge progresses so does additional classification and it is now contended that the Apiaceae family may be further divided into three subfamilies and twelve tribes (Downie 2003). As Foeniculum vulgare is the smallest genus in the family it is not surprising that it is the least studied, but as it continues to invade natural areas research is steadily advancing. However, for the most part the goal is to find effective eradication measures and not to build a phylogenetic framework for the species.

The order Apiales, that is part of the Eurasterids II clade, is subdivided into three families: Apiaceae, Araliaceae and Pittosporaceae. The Apiaceae family can then be broken down into 300 genera including Foeniculum vulgare P. Mill. The only species in the genus Foeniculum vulgare P. Miller is Foeniculum vulgare (sweet fennel).  http://www.bio.psu.edu/Courses/bio414/Asterids.html DePamphillis (2003)

Distribution and Habitat  

Foeniculum vulgare is native to southern Europe where it has been cultivated for centuries (Garland 1979), but is now found throughout the Mediterranean region and temperate climates in the western hemisphere where it has proliferated after repeatedly escaping cultivation. As with most genera in the Apiaceae family, Foeniculum vulgare is eurytopic and distribution in temperate regions with dry, warm summers and cool, moderately moist winters is continuous and nearly cosmopolitan. Reproduction easily occurs through root division and seed germination and may take place at any time of the year. Although plants will not flower until they mature between 18 months to 2 years after germination (Bean and Russo 1988), seed dispersal methods ranging from animal droppings and carriage by waterways, to ejection from agricultural machinery and automobiles are highly effective (Klinger 2000). While many organisms utilize Foeniculum vulgare as a food source, they are not necessary for survival because each plant continuously self-pollinates while flowering and finally produces copious amounts of seeds. Moreover, seeds remain viable for several years and will germinate in full sun without groundcover and little moisture. Additionally, Foeniculum vulgare tolerates a wide range of soil types, is drought tolerant and grows easily in disturbed areas where it is extremely difficult to eradicate once it becomes established. Distribution is limited in Mediterranean climates only by frost and elevations greater than 1000 feet (University and Jepson Herbaria Homepage 1993).

 Introduction into California is not well understood; however, Foeniculum vulgare has been observed in the state for at least 120 years (Robbins, et al 1941). It is found mostly in disturbed areas near brackish or fresh water, where well-drained soils ranging in Ph levels from 4.8-8.3 are present (Klinger 2000). It is common in open areas such as grassland and coastal scrub habitats, as well as hillside pastures and areas where grazing or plowing have recently occurred. Dense thickets may be observed at riverbanks, roadsides, and vacant lots in coastal areas throughout California especially on Santa Cruz Island, and in parts of San Diego and Los Angeles Counties and the San Francisco Bay Region (Klinger 2000).

Foeniculum vulgare may be observed in disturbed areas, especially near streams and in coastal regions, throughout all highlighted areas. ©Copyright 1993 by the Regents of the University of California

 Problems   

The presence of Foeniculum vulgare in California is troublesome for several reasons. Due to its eurytopic nature it easily encroaches upon native flora, depriving other plants critical to ecosystems of essential nutrients, moisture, space and sunlight. The formation of tall, dense thickets not only prevents native plants from flourishing but in some cases local fauna is also impacted. On Santa Cruz Island in the Channel Islands Foeniculum vulgare provides camouflage and shelter for introduced feral pigs that inhabit the island and are threatening the Santa Cruz Island Fox (Urocyon littoralis santacruzae) population. Currently projects are underway to eradicate the pigs from the island to preserve the fox, and eradication of Foeniculum vulgare is an integral part of that process. Research is now in progress to find the most effective removal techniques and it seems that herbicides will be the most successful method for permanent eradication from the island, but it may take as long as four years to complete the process. Unfortunately, eradication of Foeniculum vulgare may improve conditions for some native species at the expense of others. The Anise Swallowtail butterfly is now common in the western United States and Canada and relies on plants in the Apiaceae family as both a host plant and food source. Since the introduction and invasion of California by Foeniculum vulgare populations of native Apiaceae species have dwindled and the swallowtail has come to rely heavily on fennel as a consequence. The effective removal of Foeniculum vulgare may be to the detriment of the Anise Swallowtail. Foeniculum vulgare is also troublesome in wetland areas where restoration projects are currently in progress. Due to the delicate nature of wetland ecosystems and their proximity to important waterways such the San Francisco Bay, herbicides are not an option and the plants must removed by hand. This process is labor intensive, time consuming and not extremely effective. It is likely that as time and knowledge advance we will come to find more problems associated with both the invasion and eradication of Foeniculum vulgare in the state of California and only as science progresses can we hope to find a balanced plan to preserve and protect our native species.

"Fennel Boulevard" © John M. Randall/The Nature Conservancy

Bibliography
Bean, C. and M.J. Russo. (October 17, 1988). Element Stewardship Abstract for Foeniculum vulgare. [Online]. Available:  http://tncweeds.ucdavis.edu/esadocs/documnts/foenvul.html [October 1, 2003]

Brenton, R.K. and R.C. Klinger. 2002. “Factors Influencing the Control of Fennel (Foeniculum vulgare Miller) Using Triclopyr on Santa Cruz Island, California, USA.” Natural Areas Journal 22(2): 135.

DePamphillis, C. (2003). Asterids. [Online] Available: http://www.bio.psu.edu/Courses/bio414/Asterids.html. Penn State Department of Biology. [9 November 2003]  (Asterids Cladogram)

De Ruff, Robert. (September 1999). Sweet Fennel. [Online] Available: http://mamba.bio.uci.edu/~pjbryant/biodiv/PLANTS2/Apiaceae/Foeniculum_vulgare.htm. [October 13, 2003]

Downie, S. (2003). Apiaceae (Umbelliferae) Subfamily Apioideae. [Online] Available: http://www.life.uiuc.edu/downie/apiaceae.html. [8 November, 2003]

Downie, S.R., D.S. Katz-Downie and K. Spalik. 2000. “A Phylogeny of Apiaceae tribe Scandiceae: evidence from nuclear ribosomal DNA internal transcribed spacer sequences.” American Journal of Botany 87(1): 76-95.

Franco, M., J.L. Harper and J. Silvertown. 1997. Plant Life Histories; Ecology, Phylogeny and Evolution. Cambridge, U.K. Cambridge University Press.

Garland, S. 1979. The Complete Book of Herbs and Spices. Viking press, New York, NY.

Iwatsuki, K. and P.H. Raven, Eds. 1997. Evolution and Diversification of Land Plants. Tokyo, Japan. Springer.

Klinger, R. 2000. “Foeniculum vulgare Miller.” pp. 198-202. In Bossard, C.C., M.C. Hoshovsky and J.M. Randall. Invasive Plants of California’s Wildlands. Berkeley and Los Angeles: University of California Press.

Lundberg, J. (2001). Phylogenetic Studies in the Euasterids II With Particular Reference to Asterales and Escalloniaceae. [Online] Available:  http://publications.uu.se/uu/fulltext/nbn_se_uu_diva-1597. [8 November, 2003] (PDF)

Missouri Botanical Garden. (2003). Angiosprem Phylogeny Website. [Online] Available: http://mobot.org/MOBOT/Research/Apweb/orders/apialesweb.htm. [1 November, 2003].

Robbins, W.W., M.K. Bellue, and M.S. Ball. 1941. Weeds of California. California Department of Agriculture, Sacramento, CA.

University and Jepson Herbaria Homepage. (1993). Foeniculum. [Online] Available: http://ucjeps.berkeley.edu/cgi-bin/get_JM_treatment.pl?329,407,408. [8, November, 2003]

University of California, Berkeley Museum of Paleontology. (2003). Introduction to the Apiales. Available: http://www.ucmp.berkeley.edu/anthophyta/asterids/apiales.html. [9 November, 2003]

U.S. EPA. (2002). Final Environmental Impact Statement for Santa Cruz Island Primary Restoration Plan Channel Islands National Park Santa Barbara County, CA Notice of Availability. [Online] Available: http://www.epa.gov/EPA-IMPACT/2002/September/Day-03/122372.htm. [8 November, 2003]

With, K.A. 2001. “The Landscape Ecology of Invasive Spread.” Conservation Biology16(5): 1192-1203.
 

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