©The World Botanical Associates Web Page
Prepared by Richard W. Spjut
January 2005, Feb 2014

     Thamnosma is a small genus of ~11 species with a spotty distribution, occurring in southern Africa, Arabia, Socotra and southwestern North America (Spjut 2005; Thulin 1998 for African species). In southwestern North America,  Thamnosma texana (A. Gray) Torr. occurs from south-central Arizona to Sonora, to western Texas, and T. montana is found in western Arizona to western edge of the Sonoran Desert in California and also in the eastern Mojave Desert to Death Valley Region.   Thamnosma trifoliata I. M. Johnst. is known from the type locality along the southern Gulf coast of Baja California in the vicinity of Bahía de Aqua Verde (Wiggins 1980); T. stanfordii I. M. Johnst. and T. pailensis M. C. Johnst. are known from southern Coahuila, Mexico.

     Thiv et al. (2010) concluded that the species attained their present day distribution by long distance dispersal from mainland Africa to Socotra and to the New World, possibly during the Miocene.

     Africans have smoked plants of T. africana Engl. to relieve chest conditions (Watt & Breyer-Brandwijk 1962). A decoction of the stems of T. montana Torr. & Frem. has been used by Native American tribes of Nevada for colds and as a tonic (Train et al. 1957), and by other native American Indians as a laxative, hallucinogen, snakebite remedy, smallpox, for treating gonorrhea (Moerman 2009. Both species have been screened by the NCI; neither was active.



Thamnosma montana
Mojave Desert, CA
May 1973


Thamnosma montana
Mojave Desert, CA
Mar 2005


Ahua, K.M., J. R. Ioset, A. Ransijn, J. Mauel, S. Mavi and K. Hostettmann. 2004. Antileishmanial and antifungal acridone derivatives from the roots of Thamnosma rhodesica.  Phytochemistry. 65(7): 963–968.  “Eight furanocoumarins, one coumarin and four acridone derivatives have been identified in the roots of Thamnosma rhodesica (Rutaceae). Rhodesiacridone, one of these acridone derivatives, is reported here for the first time. Its structure was elucidated by spectrometric methods including ESI-HR, EI, DCI mass spectrometry, 1H, 13C and 2D NMR experiments. This novel compound showed activities against the intracellular form of a human pathogen, the protozoan parasite Leishmania major. Two known acridone related compounds, gravacridonediol and 1-hydroxy-10-methylacridone, exhibited activities against the intracellular form of the same parasite and the fungus Cladosporium cucumerinum, respectively.”

Chang P.T., G. A. Cordell, G. H. Aynilian, H. H. Fong and N. R. Farnsworth. Alkaloids and coumarins of Thamnosma montana. 1976. Lloydia 39: 134–140. “From the turpentine broom, Thamnosma montana, four alkaloids and three coumarins were isolated and characterized. Skimmianine (5), N-methyl-acridone (4) and 5-(3'-methyl-2',3'-dihydroxybutanyl)-8-methoxypsoralen (1) were obtained previously from T. montana. Robustine (2) is reported from a Thamnosma species for the first time and acridone (6), thamnosmonin (9), and thamontanin (14) are reported from a natural source for the first time. Evidence for the structures of the new isolates is presented.”

Crosby, D. G. 1954.  The Structures of Phytotoxic Compounds from Thamnosma montana. Ph.D. Thesis. Furanocoumarins, isopimpinellin and byangelicin were reportedly isolated.

Mafokane, H. F. N. Potgieter, and T. Van Ree. 2006. The compounds and biological activity of Thamnosma africana. Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie 25: 138–148.  The aerial parts and fruits of Thamnosma africana were investigated for chemical compounds present in them. The volatile oil of T. africana was prepared by hydrodistillation of leaves, flowers and stems, and characterized by GC-MS. The oil was tested for antimicrobial activity on cultures of E. coli, B. subtilis and S.aureus, and found to inhibit Bacillus subtilis and Staphylococcus aureus at 0.1% dilution. The oil was also active against Plasmodium falciparum in micromolar concentrations. Chromatographic separation of the ethyl acetate extract of the aerial parts yielded two isomers of methoxypsoralen (xanthotoxin and bergapten) and 6-(1c,2c-dihydroxy-3c-methyl-3c-butenyl)-7-methoxychromen-2-one (thamnosmonin). The epoxide of thamnosmonin, 6-(1c,2c-epoxy-3c-methylbut-3c-en-1c-yl)-7-methoxychromen-2-one (thamnosmin), and methyl p-isopentenyloxycinnamate were isolated from the hexane extract of the fruits, while another furanocoumarin, 4,9-dimethoxy-7H-furo[3,2-g]benzopyran-7-one (isopimpinellin) was isolated from a dichloromethane extract of the aerial parts.

Moerman, D. E. 1998. Native American Medicinal Plants.  An ethnobotanical dictionary. Timber Press, Portland.

Oertli E.H., E. H. Bier, G. W. Ivie, and L. D. Rowe.  1984. Linear furocoumarins and other constituents from Thamnosma texana.  Phytochemistry 23: 439–441. “Eight linear furocoumarins were isolated and identified from T. texana. They were xanthotoxin, imperatorin, bergapten, alloimperatorin methyl ether epoxide, heraclenin, isopimpinellin, psoralen and oxypeucedanin. Three coumarins wre identified: herniarin, osthol and thamnosmin. The linear furocoumarins appear to be agents that account for the known photosensitizing properties of T. texana (blisterweed).

Oertli E.H., L. D. Rowe, S. L. Lovering, G. W. Ivie and E. M. Bailey.  1983. Phototoxic effect of Thamnosma texana (Dutchman's breeches) in sheep.  Am. J. Vet. Res. 44(6): 1126–1129.  “Oral exposure of sheep to the airdried, aerial portions of Thamnosma texana (Dutchman's breeches) resulted in severe photosensitization. Sheep fed the plant at 9 or 12 g/kg of body weight/day and held in direct sunlight exhibited signs of phototoxicosis within 24 to 48 hours. The clinical signs manifested were increased body temperature; photophobia; edema of the muzzle, ears, and vulva; keratoconjunctivitis with edema of the cornea; and exudative dermatitis of the skin of the ears, muzzle, and vulva. Lesser dosages of the plant produced similar effects after several days, except that corneal edema and opacity were not seen. Histopathologic studies indicated no hepatic lesions, consistent with primary photosensitization. The photosensitizing effects of T texana can be attributed to the presence of photosensitizing linear furocoumarins (psoralens) in the plant.

Spjut, R. W.  2005.  Relationships between plant folklore and antitumor activity: An historical review.  Sida 21: 2205–2241.  "The National Cancer Institute’s (NCI) record of plants that have shown significant inhibitory effect in experimental tumor systems (active plants), 1960–1974, was compared with species and genera in references on medicinal folklore, including poisonous plants, to determine whether their percentages of active plants were significantly greater than those screened at random (10.4%). The percent active species in medicinal and/or poisonous references in general were found to be 1.4 to 2.6 times greater, while the number and different kinds of medicinal uses appear related to geographical data of species that also indicate medicinal plants were screened more thoroughly because of their widespread occurrence. The best correlation is seen with poisonous plants, including medicinal plants that suggest a moderate to strong therapeutic effect; their percentages of active species were nearly three (29.3%, anthelmintics) to four times (45.7%, arrow and homicidal poisons) greater than plants screened at random. Selection of plants based strictly on use in folk medicine would probably benefit new (start-up) screening programs, whereas in the long-term, it appears more cost effective to systematically screen the broadest diversity of plants readily available since the common medicinal species would be collected irregardless. A systematic collection strategy could give emphasis to genera that have not been exhaustively studied, especially to species with medicinal uses that indicate toxicity or ”are considered poisonous.”

Thulin, M. 1998. Thamnosma (Rutaceae) in Africa. Nordic J. Bot. 19: 5–11.  The African members of the remarkably disjunct Afro-American genus Thamnosma are revised. Six species are recognized, T africana, T. rhodesica and T. crenata in southern Africa, and T. somalensis, T. socotrana and T. hirschii in the Horn of Africa region, including the southern part of the Arabian Peninsula and Socotra. T. somalensis, sp. nov., is described from north-eastern Somalia. T. crenata, comb, nov., is based on T. africana var. crenata. A key to the species is given and two lectotypes and one neotype are selected.

Thiv, M., T. Brune, H. P. Linder, M. Thulin, T. van der Niet, and F. Rutschmann. 2011.  Old–New World and trans-African disjunctions of Thamnosma (Rutaceae): Intercontinental long-distance dispersal and local differentiation in the succulent biome. Am. J. Bot  98: 76–87 “Premise of the study: The succulent biome is highly fragmented throughout the Old and New World. The resulting disjunctions on global and regional scales have been explained by various hypotheses. To evaluate these, we usedThamnosma, which is restricted to the succulent biome and has trans-Atlantic and trans-African disjunctions. Its three main distribution centers are in southern North America, southern and eastern Africa including Socotra.  Methods: We conducted parsimony, maximum likelihood, and Bayesian phylogenetic analyses based on chloroplast and nuclear sequence data. We applied molecular clock calculations using the programs BEAST and MULTIDIVTIME and biogeographic reconstructions using S-DIVA and Lagrange. • Key results: Our data indicate a weakly supported paraphyly of the New World species with respect to a palaeotropical lineage, which is further subdivided into a southern African and a Horn of Africa group. The disjunctions in Thamnosma are mostly dated to the Miocene. Conclusions: We conclude that the Old–New World disjunction ofThamnosma is likely the result of long-distance dispersal. The Miocene closure of the arid corridor between southern and eastern Africa may have caused the split within the Old World lineage, thus making a vicariance explanation feasible. The colonization of Socotra is also due to long-distance dispersal. All recent Thamnosma species are part of the succulent biome, and the North American species may have been members of the arid Neogene Madro-Tertiary Geoflora. Phylogenetic niche conservatism, rare long-distance dispersal, and local differentiation account for the diversity among species of Thamnosma.

 Train, P., J. R. Henrichs  and W. A.. Archer.  1957. Medicinal uses of plants by Indian Tribes of Nevada.  Contributions toward a flora of Nevada, No. 45.  Revised ed. with summary of pharmacological research by W. A. Archer.  A series prepared through the cooperative of the National Arboretum and the Plant Introduction Section, USDA, ARS, Beltsville, MD.

Watt, J. M. & M. Breyer-Branwijk. 1962.  The Medicinal and Poisonous Plants of Southern and Eastern A6rica.  2nd Ed.  E & S Livingstone, Ltd., Edinburgh & London.

Wiggins, I. 1980. Flora of Baja California. Sanford University Press.