A Preliminary Account of the Aquatic and Sub-Aquatic Vegetation and Flora of the Witwatersrand

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Abstract
The area studied extends from Florida, 9 miles west of Johannesburg, to Brakpan, 23 miles east of this city. The sheets of water may be classified as follows: (1) Artificial dams, usually in connection with the gold mines, and, as a rule, of little botanical interest. (2) Semi-natural lakes, made by the artificial damming up of streams. Reed swamps occur, with the following plants locally dominant: Typha australis, Phragmites communis, Scirpus macrocarpus, and Cyperus fastigiatus. Of plants with floating leaves, Limnanthemum thun-bergianum is abundant in one of the lakes. Submerged plants occur, such as Potamogeton javanicus, P. badius, and a new, undescribed, sp. of Potamogeton. The margin is rich in marsh spp., including Juncus effusus, J. spp., Ranunculus sardous, R. meyeri var. transvaalensis, Nasturtium offidnale and Epilobium villosum. A new, undescribed var. of Spergulana marginata occurs. (3) Natural sheets of water, which are: (a) Pans, or shallow depressions whose origin is in dispute. They are frequently dry in winter. They have a typical and characteristic marginal flora, with Spergularia (aff. S. salina), Lessertia sp. nov., Cuscuta sp. nov., and others. Lemna minor, L. gibba, and Wolffia arrhiza occur locally in the pans of the East Rand. Potamogeton pectinatus var. and Zannichellia pedicellata occur in Brakpan. The pans have a rich plankton, consisting chiefly of copepods and diatoms. Volvox rousseleti and Hydrodictyon indicum (?) occur in Rietfontein pan. The pans have no streams flowing out of them, and consequently their mineral content is high, becoming almost supersaturated as the dry season approaches. Incrustations of salts are common on the receding margins of the pans, as the water evaporates. (b) Streams and their backwaters. The backwaters have the same flora as the lakes; and the stream banks yield the same plants as the margins of the lakes.

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