Structures Of Vegetative Organs, Floral Development In Typhales, And Their Evolutionary Implications

Typhales contains two genera, Sparganium and Typha. It is a widely distributed order of Monocotyledopsida which has rather few species. There has always been much argument over its systematic position as well as different views about the evolutionary relationship between Sparganium and Typha. The vegetative organs are anatomically studied, the development of floral organs is observed in this paper. Then there is a discussion on the systemic evolution of Typhales based on available data.The structural features of roots, rhizomes, stems and leaves,are studied by means of paraffin sections. With observation of different developmental phases and positions of leaves, it is inferred that the leaf structure of Typha may have evolved from that of Sparganium. The structure of oots, rhizomes and stems in the two genera quite resemble each other. The layer of fiber cells, which might feature the order, divides the parenchyma in stems into two parts. All the vegetative organs have gas chambers or at least aerenchyma. This means that plants in the order have long been adjusted to aquatic or marshy environments.The processes of flower development of Typha angustifolia Linn, and Commelina Setcreasea purpurea Boom., which respectively represent Typha and Commelinales, are observed and compared with that Sparganium. There are significant resemblances between Sparganium and Typha whereas their tepal development shows remarkable differences. Also mature flower structure of Commelinales and Typhales bears no resemblances.The view is affirmed further in this paper that Sparganium and Typha are closely related, and the former is more primitive. At the same time Typhales is not considered to originate immediately from Commelinales. It might be related to Commelinidae, but differentiated away from common ancestors early.