DATE PALM ALLIES IN AMERICA 



North American Fan Palms Related to the Genus Phoenix — Several Mexican 



Species With Date-Like Fruits — Majority of Palm Families 



Native to New World. 



O. F. Cook 

 Bureau of Plant Industry, U. S. Department of Agriculture, W'asJiington, D. C. 



THE finding of fossil date sscds 

 in eastern Texas is an interest- 

 ing discovery recently an- 

 nounced by Dr. E. W. Berry/ 

 As date palms have been known hitherto 

 only in the Old World, it may be worth 

 while to call attention to the analogies 

 presented by some of the native Ameri- 

 can fan-palms. The geographical ob- 

 stacles to the recognition of such an 

 alliance being removed by the discovery 

 of the fossils, two questions naturally 

 suggest themselves. Is the finding of 

 these fossils to be taken as an indica- 

 tion that the date palm, or the genus 

 Phoenix, originated in America, and 

 which of the existing genera is to be 

 looked upon as the nearest surviving 

 relative of Phoenix in America? 



It has long been recognized that 

 Phoenix is much more closely related to 

 the fan-palms than to other pinnate- 

 leaved palms. Even the leaf structure 

 shows that there is no alliance with the 

 other pinnate palms, for in comparison 

 with these the pinnae of Phoenix appear 

 to be reversed, or up-side-down, being 

 V-shaped in cross-section, whereas in 

 all other pinnate palms the pinnae are 

 A-shaped, as though folded down in- 

 stead of up. This difference becomes 

 very significant when we recognize the 

 probability that the two forms of 

 pinnae represent different methods of 

 splitting an ancestral undivided, plicate 

 or plaited leaf. 



A plicate leaf split along the upper 

 folds or ridges gives V-shaped segments. 

 Splitting along the grooves between the 

 ridges would result in reversed or 

 A-shaped segments. These considera- 

 tions are not altogether theoretical, in 



view of the fact that the seedlings of 

 nearly all palms have undivided leaves. 

 The mature, compound form of leaves 

 is attained usually by very gradual 

 stages of increasing the number of 

 segments and splitting them apart. In 

 all of the fan-palms that have deeply 

 divided leaves the splitting takes place 

 along the grooves, resulting in V-shaped 

 segments, like those of the date palms. 

 Hence we may consider that the 

 specialization of the date palm leaf 

 consists mostly in the addition of an 

 elongated rachis or midrib that allows 

 the segments or pinnae to stand well 

 apart, instead of being inserted on a 

 central base, or ligule, like the radiating 

 segments of the fan-palms. The leaves 

 of some of the fan-palms show no indica- 

 tion of a midrib, as in the genus Thrinax 

 and its relatives. But in most of the 

 genera the middle segment of the leaf 

 has a thickened midvein or rudimentary 

 rachis. Some of the American palmetto 

 palms present an intennediate type of 

 leaf structure, with a more strongly 

 developed midrib. The leaves of Inodes 

 are of an oval form, and with a part of 

 the segments inserted on a strong, 

 decurved midrib, as shown in fig. 8. 

 A further development of the midrib, 

 sufficient to separate the segments, 

 would afford a transition to a pinnate 

 leaf, with a structure parallel to the 

 leaves of the date palms. Hence we 

 may say that as far as leaf structure is 

 concerned the genus Inodes offers an 

 analogy with the date palms. 



PHOENIX AND PSEUDOPHOENIX. 



As the name indicates, the genus 

 Pseudophoenix also presents certain 



1 Fruits of a Date Palm in the Tertiary Deposits of Eastern Texas, American Journal of Science, 

 37:403, 1914. 



117 



