The taxonomy and nomenclature of Rutaceae-Aurantioideae

Prom the time of CORREA DE SERRA (1805), MIRBEL. (1813), DE JUSSIEU (1815), ROEMER (1846), BAILLON (1855), and OLIVER (1861), a great stress is laid upon the number of stamens, locules, and ovules to the primary classification of the Rutaceae-Aurantioideae, but the importance of the presence of an inflorescence and its reduction of the number of flowers, the pinnate leaf and its reduction of the number of leaflets, venation of the leaf, its conspicuousness and the construction, the origin and development of the wing upon the rachis and the petiole, the number and the nature of thorns upon the branches, the fundamental number of the floral organs and its increase or decrease, the formation of pulp vesicles, the hardening of the rind of fruits, and other points affecting the universal affinity of plants as a whole, have been quite neglected in the past, the consideration of which would have helped the orderly development of the taxonomy of the subfamily. It is clear that the increased number of the floral organs and the development of the pulp vesicles are undoubtedly very important systematic features of the subfamily, but such are those out of many significant characteristics which take part in the classification of the whole group. A character like the increase or decrease of the number of locules, for instance, can occur even within one genus, as in the well-known case of Citrus and Fortunella. The ovules may be single, or binary, either superposed or collateral, or otherwise numerous in uni-, or biseriate arrangement: the gradation of this character is also continuous, as in the case of Merope Triphasia, and Wenzelia, all having similar floral characteristics but the last only has biseriate ovules. Unquestionably, the biseriate character is derived from collateral arrangement which is commoner in rather advanced groups. The increase of the number of filaments more than ten, occurs also in tribes not closely related, as Aegle (also Feroniella, and Balsamocitrus Section Afraegle), Oxanthera, and Citrus (also Poncirus and Fortunella), but the true pleiotaxy of stamens occurs only in Aegle and in the Section Citrophorum of the genus Citrus. The pulp-vesicle formation is also seen in various tribes widely divergent from each other, such as Aegleae-Swingleinae (Swinglea), Lavangeae (Pleiospermium), Atalantieae (Atakmtia and Severinia), Microcitreae (Microcitrus, Eremocitrus, Monanthocitrus and Pleurocitrus), Aurantieae-Citropsinae (Citropsis), and Aurantieae-Citrinae (Poncirus, Citrus and Fortunella). It is very clear that the starting point of the subfamily is represented by Micromelum and Glycosmis, both having pinnate leaves with alternate leaflets and unwinged rachis, many-flowered inflorescences, an ovary with less than 5 locules and one or two superposed ovules in each locule. Having dry fruits and contortuplicate cotyledons, Micromelum forms the most primitive tribe Micromeleae, somewhat analogous to the Rutoideae-Cusparieae of tropical America. The genera Glycosmis, Murraya and Clausena, altogether forming the tribe Clauseneae, have fleshy fruit, plano-convex cotyledons and unarmed branches with pinnate leaves, resembling the Micromelum in general appearance of the plant. It is worthy of note that the great reduction of the number of leaflets is seen in such species, as Micromelum diversifolium MIQ., Clausena Guillauminii TANAKA, and Murraya stenocarpa TANAKA (= Chalcas stenocarpa TANAKA) , and the alate rachis is found in Clausena Wallichii OLIV., C. Guillauminii TANAKA and Murraya alata DRAKE. The reduction of the number of locules in Murraya is also to be noted. No thorn-bearing plants occur in these tribes, except in the doubtful species, Clausena impunctata HIERN, which has curved paired axillary spines, almost entirely opposite leaflets, and a distinctly winged rachis. The gradation of this tribe into the next tribe Aegleae, having hard-shelled fruits, is seen in the Malayan genus Merrillia, which has large flowers, reminding of Murraya (Subgen. Euchalcas TANAKA), and a winged rachis like M. alata, mentioned above.