Studies in the Phylogeny of the Betulaceae. I. Floral and Inflorescence Anatomy and Morphology

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Abstract
A study of the morphology and vascularization of the cymules and florets of 64 spp. and vars. of the Betulaceae from each of the genera and subgenera indicates the following: (1) The morphology and anatomy of the cymules and florets has been notably modified by dorsiventral or lateral concrescence, shortening of internodes, pressures within the ament, and reduction; (2) the bicarpellary ovaries owe their transverse or diagonal orientation to their derivation from an ancestral tri-carpellary ancestor, while the staminate florets in some spp. still are trimerous; (3) the full complement of bracts is present in the pistillate cymules of Carpinus, Ostryopsis, and Ostrya, the adaxial tertiary bract is lost from the staminate and pistillate cymules of most species of Alnus. Both adaxial and abaxial tertiary bracts have been lost from the staminate cymules of Betula, Corylus, Carpinus, Ostrya, and from the pistillate cymules of Betula. The secondary bracts have been lost, while the tertiary persist, in the pistillate cymules of Corylus. All bracts but the primary have been lost in the staminate cymules of Ostryopsis. (4) The staminate cymule is 3-flowered in all genera of the family. The pistillate cymule is 2-flowered by suppression of the secondary floret in all genera except Betula, in which all 3 florets are present. (5) The perigon is present in the pistillate florets of Carpinus, Ostrya, Corylus, Ostryopsis, and in the staminate florets of Alnus and Betula; it is obsolescent in the pistillate florets of Alnus and Betula; it is completely lost from the staminate florets of Carpinus, Corylus, and Ostryopsis. The ovary is inferior throughout the family.

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