CLASSIFICATION OF MONOCOTYLEDONS 233 



pels and the stamens are connate ; while in the carpellate flowers 

 there are very conspicuous and often branching staminodia. 

 There is a strong tendency to " coalescence " in all the members, 

 the perianth often being tubular, the stamens usually connate, 

 and the carpels (if more than one) always forming a syncar- 

 pous pistil. The group is also peculiar in the very numerous 

 ovules upon a single parietal placenta. 



Too little is known of the morphology of the group to speak 

 of its relationships with any definiteness, but it seems safe to 

 regard it as another branch of the Pandanales stock. The Pan- 

 danales, Palmales, and Synanthales are thus referred to a com- 

 mon origin, with the Pandanales as the most primitive repre- 

 sentative of the stock. This tropical association seems to be a 

 strange one for Typha and Sparganium, but otherwise it seems 

 to be entirely natural, and not clearly related to any other ]\Iono- 

 cotvledons. 



VI. Aeales.* — This includes the Araceae with about 1,000 

 species, and the Lemnaceae with about 25. The Aroids form 

 one of the most distinct and also diversified groups of Monocot- 

 yledons. The characteristic features are the spadix, the highly 

 developed spathe, and the broad net-veined leaves. There is 

 also probably greater anatomical differentiation than in any 

 other monocotyledonous group, which is taken advantage of 

 in their classification. The floral structure is of three general 

 types: (1) the Calamus type, in which the flowers are bisporan- 

 giate, pentacyclie, 2 to 4-merous, and syncarpous ; (2) the Calla 

 type, in which the flowers are bisporangiate, with no perianth, 

 6 to '•» stamens, and 1 carpel; (3) the Arum type, in which 

 the flowers are monosporangiate (staminate flowers above and 

 • •arpellate flowers below on the same spadix), and with no 

 perianth. 



It is evident that the floral structure is extremely fluctua- 

 ting, and that this is probably associated with the extreme spe- 

 cialization of the spathe. Engler has called attention to the 

 fact that the flowers with a perianth are associated with a 

 bract-like spathe; while those without a perianth (the great 

 majority) are associated with a petaloideous spathe. In any 

 event, the bract reaches its highest specialization in this group, 



* Spathiflorae of Engler. 



