1960] 



SPATHIPHYLLUM 



5 



occurs mostly in species of sect. SpathiphyUum. The number of primary lateral 

 veins and the angle at which they arise from the midrib seem to be constant 

 features valuable in identification. 



Petiole. Though the petiole is similar in most species, the geniculum 6 may be 

 exceptionally long or occasionally alate. 



Inflorescence. The length/width ratio and the shape of the spathe are 

 essentially constant for a species. Texture of the spathe is rarely an important 

 species characteristic. In most species, color of spathe varies with age of 

 inflorescence. 



The spadix (as a unit) has little taxonomic value. In many species, it is borne 

 on a free stalk, here called the stipe ; this term always refers to the more or less 

 terete, free apical portion of the peduncle between the point of attachment of the 

 spathe on the peduncle and the base of the spadix. The length of the stipe is 

 sometimes a good diagnostic characteristic. 



Flowers. The perianth furnishes adequate sectional differences only, except 

 in two species in which the apex of the perianth is distinctively modified. This 

 characteristic has not been previously recorded. In most other works on aroids. 

 the perianth segments are designated as sepals or tepals. Since the 4-6 (-7) 

 perianth segments occur in a single series in SpathiphyUum, the terms "perianth" 

 and "perianth segments" are used throughout this paper. 



Specimens were examined in which the stamens appear to be of reduced size, 

 but my study of these structures was inconclusive because of the small amount 

 of material and the variability in the size of the stamens within a single flower 

 (Fig. 2B). 



The pistil may be attenuate and exserted beyond the perianth, or inflated, 

 annular, and/or truncate and scarcely exceeding the perianth. The proportional 

 length of the exserted portion in respect to the length of the perianth may 

 characterize a species, but more commonly a group of species, or a section. 



Ovary differences, relied upon heavily by Engler and others for separation 

 of species of SpathiphyUum, are of limited taxonomic value in this genus. In 

 some species the number of locules per ovary is reduced from the usual three to 

 two, yet the bilocular situation may result by abortion only in some individual 

 flowers of a spadix. In his key to the species, Engler emphasized the number of 

 ovules per locule. My investigations have shown that this characteristic may 

 be misleading. The number of ovules is sometimes inconstant from flower to 

 flower and plant to plant. Moreover, the number of ovules in the locules of a 

 single pistil is not equal ; one locule tends to have one or occasionally two ovules 

 more than the others. The largest number of ovules in any locule is significant, 

 a smaller number simply indicating that a reduction has occurred. 



6 The geniculum is the thickened dist.il end of the petiole found in several genera of 

 Araceae and in other families. 



Fig. 2. A-D. Keproductive structures typical of species of SpathiphyUum sect. Spathiphyl- 

 lum. A. Inflorescence (somewhat reduced). B. Flower, X 10- C. Longitudinal section of 

 pistil. D. Fruit, X 6. E. Inflorescence typical of species of sections Massowia, Amomophyl- 

 lum, and Dysspathiphyllum (somewhat reduced). F-H. Eepreduceive structures typical of 

 species of sect. Amomophyllum. F. Flower, X 10. G. Longitudinal section of pistil. H. 

 Fruit (also typical of species of sect. Massoivia) , X 6. J. Flower typical of species of sect. 

 Massowia, X 10. K. Flower of S. humboldtii (sect. Dysspathiphyllum) , X 10. L. Seed with 

 more or less smooth surface, X 12. M. Seed with furrowed and verrucose surface, X 12. 



