University Herbarium, UC Berkeley
DRAFT - July 1999


Barbara Ertter
Curator of Western North American Flora
University and Jepson Herbaria
University of California at Berkeley, USA

In May 1999, the unique opportunity presented itself to travel to Iran, essentially off limits to Americans for the last two decades, with invitations to speak at the agricultural colleges at several universities. The following essay is adapted from the talk I chose to present, comparing the biogeography of western North America (my personal area of expertise) with Iran, and ending with an illustrated overview of the biogeographic regions of western North America.


To fully understand the evolution and relationships of a floristic area, it helps considerably to make comparisons with similar floras in other parts of the world. Iran is uniquely suitable for comparing with western North America, as a result of numerous geographic, climatic, and geological similarities:


Along with climate, geology, and topography, which are primary factors that determine plant distribution, similarities between the floras of Iran and western North America are increased by historical biogeography. Both regions contain remnants (refugia) of the broad leaf forests that once covered most of the north temperate zone 25 - 50 million years ago, in the early Cenozoic Era. As the climate and land forms changed, this forest disappeared from most of its former range, being replaced by shrublands, grasslands, deserts, and conifer woodlands. The two main areas where the mesophytic forest has persisted are southeastern Asia and southeastern North America, but smaller pockets also exist in northern Iran (Hyrcanian forest) and along the west coast of North America.
During the Pleistocene ("Ice Ages"), glaciation had minimal impact on either western North America or Iran. Instead of the massive ice sheets that covered much of northeastern America, glaciers were largely restricted to high elevations in western North America. The more extensive Pleistocene event was the formation of large lakes in the interior-draining basins of the central plateau, most of which have now disappeared, in some cases leaving behind extensive alkaline flats. Furthermore, lowered sea levels resulted in a land bridge between Siberia and Alaska, allowing for the intercontinental migrations of cold desert floras.


As a result of the many similarities in geography, geology, climate, and biogeographical histories, over 250 genera of vascular plants occur as native in both western North America and Iran (Appendix 1). Prominent examples include Astragalus, Allium, Potentilla, Fritillaria, Viola, Eryngium, Epilobium, Trifolium, and Senecio. Several species also are apparently native in both areas, such as Galium aparine, Oligomeris linifolia, Hydrocotyle ranunculoides, and Oxyria digyna (Appendix 2).

Both regions are also noteworthy for their overall floristic richness and high degree of endemism. According to Takhtajan (1986), endemism in the Irano-Turanian floristic region is probably no less than 25%, with the richest flora being that of the Iranian Plateau. Endemism in the Madrean Region, which includes the arid and semi-arid portions of western North America, is even higher, probably well over 50%. Plants new to science are still being actively discovered and described from both areas, at an average rate of 40 vascular plants per year in western North America (Hartman & Nelson, 1998).


Although the focus of this essay is on the biogeographic similarities between western North America and Iran, it is equally important to appreciate the many differences and unique biogeographic features of both regions. For example, the interior basin of Iran is as a generality hotter and drier than that of western North America, with larger expanses of sandy deserts and salt basins. The rainfall is on the average higher in western North America, due to the proximity of the Pacific Ocean and slightly higher latitude. As a result, Iran lacks the extensive conifer forests and numerous high mountain lakes that characterize higher elevations in western North America.
Each area has also developed species-rich genera that are completely absent from the other area. In western North America, such characteristic components of the vegetation as Eriogonum (Polygonaceae), Lupinus (Fabaceae), Lomatium (Apiaceae) Phacelia (Hydrophyllaceae), Penstemon (Scrophulariaceae) and Castilleja (Scrophulariaceae), as well as the entire family Cactaceae, are not found in Iran, where one encounters instead such species-rich genera as Onobrychis (Fabaceae), Nepeta (Lamiaceae), Haplophyllum (Rutaceae), Gagea (Liliaceae), Ferula (Apiaceae), Echinops (Asteraceae), and Cousinia (Asteraceae). These are only some of the most conspicuous examples of genera that represent the differences between the two areas, differences that are as important as any similarities.


The combination of similarities and differences of two areas as comparable as western North America and Iran create significant research opportunities beyond what could be learned by studying either region alone. Comparative studies of this kind can sometimes result in critical or surprising information that might not otherwise have even been suspected.

TAXONOMIC STUDIES: At the top of the list are taxonomic studies of genera that occur in both North America and Eurasia, especially those that have radiated into numerous species. Such groups provide an excellent opportunity for comparative studies of independent radiations from common ancestral stock, posing potentially significant evolutionary and ecological questions of a general nature.
Comprehensive taxonomic studies of species throughout the entire range of a genus are particularly critical for determining the phylogeny (relationships) of species within the genus. The closest living relatives of a species do not necessarily occur in close geographic proximity, but could potentially be found in another part of the world entirely. Two excellent examples from western North America are the following:

NATURALIZED SPECIES: The biogeographic similarities that have been noted have not only resulted in the natural occurrence of numerous genera, and even some species, in both western North American and Iran, but they have also created suitable conditions for species from one area to become naturalized in the area. At least 375 species that are apparently indigenous in Iran have become naturalized in California (Appendix 3), either deliberately or unintentionally. Many of these have become serious pest plants in western North America (e.g., Avena fatua, Brassica nigra, Bromus tectorum, Centaurea solstitialis, Chondrilla juncea, Euphorbia esula, Lepidium latifolium, Lythrum salicaria, Potentilla recta, Ranunculus testiculatus, and Tamarix ramosissima), causing significant agricultural losses, outcompeting many unique native species, and threatening entire ecosystems.
Although Iran is not necessarily the primary center of distribution for any of these species, field work in Iran might potentially lead to significant insights into why species that are relatively benign members of their native ecosystems become serious pest plants in western North America. This understanding might then lead to the development of techniques to control infestations. This is an especially promising possibility in the field of biocontrol, in which the various insects and pathogens that checked infestations in the original range are deliberately introduced (after rigorous testing to determine host specificity) to provide similar control where the species has become naturalized.

COMPARATIVE ECOLOGY: By comparing the ecologies of two similar regions, questions present themselves that might not have otherwise have arisen by studying one area alone. For example, do the different impacts of cattle vs. sheep grazing contribute to the tendency of Bromus tectorum to form a monoculture in western North American, displacing the native shrub-steppe vegetation? And why are the higher elevations in Iran not forested, as they are in western North America? Is this due to climatic differences, or is it an indication of prehistoric land management practices? The answers to these kinds of questions can obviously have great significance to current land use decision-making.


As noted above, opportunities for comparative studies can have direct implications for land management issues in both western North America and Iran. This is especially apparent in agricultural practices, in which crop plants developed in one area are subsequently grown in the other. Because of the significantly longer history of intensive agriculture in Eurasia than in western North America, most of this transfer of crop plants (and associated weeds) has been from the former to the latter. This has recently become increasingly complicated by the advent of genetic engineering, which triggers a largely unresolved set of questions with legal, political, economic, and ethical ramifications.
In addition to agriculture, the economies of both regions depend heavily on other land management practices, including grazing (mostly sheep in Iran, cattle in western North America), mineral and petroleum extraction, timber production and harvest, and hydroelectric power generation. Water issues can become important in both regions, given the competing demands on a limited and finite water supply. Wild harvesting of medicinal herbs, which has a long tradition in Iran, has recently come to prominence in western North America as well.
As the population of both western North America and Iran continues to increase, all of these land management practices come into increasing conflict with the conservation of each region's rich floristic heritage. As a consequence, it may be that the most valuable long-term result of comparative studies is the insights potentially gained that can address both the needs of the human populations and the preservation of each region's richly unique natural heritage.

The remainder of the lecture presented in Iran consisted of slides showing the geography and vegetation of the following regions:


Full credit for the opportunity to visit Iran and to present the lecture on which this essay is based must be given to Dr. Fosiee Tahbaz, who solicited the original invitations and then handled subsequent arrangements with Iranian authorities. Significant acknowledgments are also earned by Dr. Brent Mishler (Director of the University and Jepson Herbaria) for his backing of the Iranian visit, and by Dr. Razani (Permanent Mission of the Islamic Republic of Iran to the United Nations) for his efforts in making the visit possible. The encouragement by Dr. Peter Raven at all stages of the undertaking has also been significant. Our hosts at the various Iranian universities, as well as the overwhelming reception by Iranian people in general, are deeply appreciated. The generous gift by V. Mozaffarian of his compilation of Iranian plant names greatly simplified comparisons of the Iranian and California floras. Airfare to and from Iran was funded by the Committee for Research and Exploration of the National Geographic Society, grant 6489-99.


Chaudhri, M.N. 1968. A revision of the Paronychiinae. Meded. Bot. Mus. Herb. Rijks Univ. Utrecht 285: 1 - 440.

Ertter, B. 1985. Paronychia ahartii (Caryophyllaceae), a new species from California. Madroño 32: 87 - 90.

Hartman, R.L. & B.E. Nelson. 1998. Taxonomic novelties from North America north of Mexico: a 20-year vascular plant diversity baseline. Monogr. Syst. Bot. Missouri Bot. Gard. 67: 1 - 59.

Hickman, J.C. (editor). 1993. The Jepson Manual: Higher Plants of California. University of California Press, Berkeley.

Mozaffarian, V. 1996. A dictionary of Iranian plant names: Latin, English, Persian. Farhang Mo'aser (publ.): Tehran.

Rollins, R. C. 1892. A new species of the Asiatic genus Stroganowia Cruciferae) from North America and its biogeographic implications. Syst. Bot. 7: 214 - 220.

Takhtajan, A. (transl. by T.J. Crovello et al.). 1986. Floristic regions of the world. University of California Press: Berkeley.