FAHY ACIDS 1 33 



UMBELLIFERAE 



A structural isomer of oleic acid, petroselinic acid, is appar- 

 ently confined to a few families including the Umbelliferae where it 

 represents a major component (for example, 75 per cent of the total 

 fatty acids in Petroselinum sativum) in most of the species tested. In 

 addition to the Umbelliferae, petroselinic acid has been found in ivy 

 {Hedera helix) of the related family, Argdiaceae. However, one other 

 plant known to produce the acid as a major component is Picrasma 

 guassioides of the family Simarubaceae. This family is not closely 

 allied with the UmbeUiferae though Meara (1958) states that petrose- 

 linic acid is confined to the members of the Umbelliferae and one or 

 two members of isolated but related species. It is significant that 

 tariric acid has been reported only from the genus Picramnia of the 

 family Simarubaceae. Petroselinic acid is an octadec-6-enoic acid 

 while tariric is an octadec-6-ynoic acid. 



PALMAE 



According to Hilditch (1952), "In both constancy and com- 

 plexity of the mixture— the seed fats of the palm family form the out- 

 standing instance of specificity of fatty acid composition within a 

 single botanical family." 



Within this family lauric and myristic acids (C12 and C14) 

 usually make up 50 per cent or more of the total fatty acid 

 complement. 



In addition shorter chain acids, such as caproic, caprylic, and 

 capric, are generally present along with palmitic, stearic, and the un- 

 saturated acids, oleic and linoleic. This group of acids represents re- 

 markable diversity with respect to carbon chain length, and in addi- 

 tion it is indicated that the relative proportions are rather constant 

 among different species and even among various genera within 

 the family. 



The fatty acids of the Palmae demonstrate the fact that 

 chemical characters may be somewhat constant within a taxonomic 

 group dehmited on other grounds. This has been shown in a number 

 of other studies involving other compounds, of course, and the fatty 

 acids of the Palmae are distinctive only in that they involve the oc- 

 currence of rather constant proportions of a series of compounds. Un- 

 fortunately, the fatty acid complement of the Palmae does not 

 provide much insight into relationships within the family or with 

 other families. 



Hilditch, a chemist, has obviously recognized that fatty acid 

 metabolism and morphological characters are often correlated, and 

 the following statement (Hilditch, 1952) illustrates at once the promise 

 and the pitfalls of phytochemical systematics: 



