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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN [Vol. 8, No. 4 



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infolded petal, stamens, and style. However, in section Stenosolen they open com- 

 pletely abaxially but only partially along the adaxiai line (Fig. le). In the less 

 highly evolved taxa the bracteoles are generally pubescent on both surfaces, but 

 in more advanced groups they are pubescent on only one surface or entirely 

 glabrous. 



Flowers. The flower is composed of a hypanthium, four or five sepals, one 

 petal, three stamens, and a single pistil (Fig. 1). The hypanthium, which is either 

 sessile or stipitate, is here quite likely the result of the fusion of the bases of 

 the filaments, the calyx, and possibly of the petal. It is either cupular or long- 

 cylindric, and this difference is of first importance in distinguishing the two sec- 

 tions. It is cylindric and regular or nearly so in section Stenosolen but cupular 

 and more or less zygomorphic in section Vouapa (Figs, la, e). 



On the margin of the hypanthium are borne the sepals, petal, stamens, and 

 sometimes the pistil as well. The calyx of section Stenosolen is regularly four- 

 parted, with lobes about equal in size and about uniform in shape (Fig. le). In 

 section Vouapa the lobes are five and free, or five with the adaxiai pair united 

 laterally to a greater or lesser extent, or four by the complete lateral union of the 

 adaxiai pair (Figs. la-d). While the number of sepals has been employed to some 

 degree in delimiting species, it has more often been neglected for more easily 

 discernible characters. In each of the phylogenetically lower taxa of section Vou- 

 apa the sepals are about equal in size, but in the more advanced forms the adaxiai 

 pair is often smaller and frequently of a different shape from the other lobes. 



The single petal, which is situated on the adaxiai side of the flower, is of two 

 general types (Figs, la, e). In section Stenosolen it is an elliptic, oval, or ob- 

 lanceolate organ, sometimes sessile or more often with a very short insignificant 

 claw. In the section Vouapa the petal is provided with a definite stipe about as 

 long as or longer than the transversely oval or orbicular blade. The term "trans- 

 versely oval" refers to an oval outline in which the long axis is perpendicular to 

 the claw. The size and form of the blade is of only moderate importance as a di- 

 agnostic character. Petalodia, that is, vestigial petals, occur. sporadically in sev- 

 eral groups, but they are so infrequent in their occurrence that they are rarely 

 mentioned in the descriptions and are of no use taxonomically. 



Of the three stamens, one is abaxial and the other two are lateral. Occasionally 

 the length of the filaments and the presence or absence of pubescence on them 

 provide the only characters of even secondary importance in delimiting taxa. They 

 are always long and slender, bearing at their apex versatile, bilocular anthers. 

 The pollen grains are trilobate, and Dr. Erdtman described their structure (in cor- 

 respondence) as follows: "On micromorphological basis the 'sexine' . . . is con- 

 spicuously striate. The striae are densely spaced in the South American species; 

 their upper surface is flat, and the extosexine (which forms the bulk of the striae) 

 is supported by short rods ('bacula'); in some species they are almost lacking.*' 



The single pistil consists of a short to long gynophore, an ovary, style, and 

 stigma (Figs, la, e). Although the tribe Amherstieae has been characterized as 

 possessing a gynophore inserted on the adaxiai wall of the hypanthium, in Macro- 

 lobium it may be thus inserted or free from the hypanthium. Below the point at 

 which the gynophore becomes free from the wall (except when it is basally in- 



Explanation of Figure 1 



FIG. 1. a. Flower of M. multijugum, a representative species of section Vouapa. b-d. 

 Adaxiai sepal pair from three species to show stages in lateral union; b. M. microcalyx, 

 X 4; c. M. multijugum, X 4; and d. M. canaliculatum, X 2; e. Flower of M. s ten o siphon, type 

 species of section Stenosolen. f. Bracteoles of M. stenosiphon showing incomplete open- 

 ing on adaxiai side of flower. 



