3. Althenia. POTAMOGETONACEAE. 47 



3. ALTHENIA, Fr. Petit. 



(After J. Althen, a Persian, who took refuge in France and introduced the cultivation of 

 madder, Eubia tinctorum, in 1760.) 



Flowers dioecious, solitary within 1-2 sheathing bracts consisting of the stipules of 

 reduced leaves ; male flower on a short pedicel, with 3 sessile, 2-celled anthers, coherent 

 by their backs so as to appear like a single ovoid, 6-celled anther, and enclosed in one or 

 two inner hyaline bracts ; at the base of the anthers are 3 small perianth -segments (or 

 bracteoles ?) ; female flower pedicellate, consisting of 3 distinct, stalked carpels, each 

 ovary tapering into a style with oblique stigma and with a scarious perianth -segment 

 (or bracteole ?) at base ; ovule 1 in each carpel ; pollen globular. Submerged plants, 

 inhabiting fresh or brackish water, with filiform stems and capillary alternate leaves 



The Australian species belong to the section Lepilaena. 



Style shorter than the overy A. australis 1. 



Style longer than the ovary A. Preissii 2. 



1. A. australis (J. Drumm.), Aschers. Female flower with styles shorter than the 

 ovaries, the perianth segments ovoid, entire, only about 1^ mm. long and shorter than 

 the carpel ; fruiting pedicels attaining a length of 2-3£ cm. — Lepilaena australis, J. Drumm. 



South-East and at least as far north as Adelaide. Sept. -Nov. 



2. A. Preissii (Lehm.), Graebn. Female flower with styles longer than the ovaries, 

 the perianth-segments oblong, bifid at summit, and as long as the young carpel (3 mm.) ; 

 fruiting pedicels exceeding the sheathing bracts, but not nearly as long as those of the 

 preceding species. — Lepilaena Preissii (Lehm.), F. v. M., and including L. cylindrocarpa 

 (Koern.), Benth. 



South-East. Sept. -Nov. 



4. POSIDONIA, Koen. 

 (From Greek Poseidon, Neptune, god of the sea.) 



1. P. australis, Hook f. Submarine plant, the base of the stem covered with the 

 fibrous remains of the leaf-sheaths ; leaves long, linear, 3-8 mm. broad, with about 9 fine 

 parallel nerves ; flowers bisexual in a compound spike with a long floral leaf at base 

 and shorter floral leaves at the base of each single spike ; no perianth ; stamens 3, the 

 connectives lanceolate, persistent and bractlike at the base of the fruit after the 2 basal 

 anther-cells have fallen ; pollen filiform ; carpel 1, sessile, contracted at summit ; stigma 

 3-4-lobed ; ovule 1, erect ; fruit about 2 cm. long, obliquely ovoid-acuminate, with 

 fleshy pericarp, dehiscing irregularly at the base. 



Sea-coast. May-Sept. 



5. POTAMOGETON, L. 



(Greek potamos, a river ; geiQn, neighbor.) 

 Flowers bi-sexual, in dense simple spikes on axillary peduncles ; perianth-segments 4, 

 broad ; stamens 4, inserted at the base of the segments, almost sessile ; pollen globular ; 

 carpels 4, free, with a rather hard endocarp when in fruit ; seed much curved. Freshwater 

 perennial plants, with alternate leaves, or opposite ones when they are under the branches 

 and peduncles. 



A. Leaves all alike, submerged, sessile or nearly so, mem- 

 branous. 



B. Leaves oblong, curly on margins P. crispus 1. 



B. Leaves narrow-linear, flat. 

 C. Leaves not sheathing. 



Leaves obtuse, 3-5-nerved P. ochreatus 2. 



Leaves acute, many -nerved P. acutifolius 3. 



C. Leaves sheathing, very narrow P. pectinatus 4. 



A. Leaves dissimilar, the upper ones petiolate, with broad 

 floating blades. 



Floating leaves with 18-25 nerves P. Tepperi 5. 



Floating leaves with about 15 nerves P. tricarinatus 6. 



1. P. crispus L. Curly Pondweed. Leaves linear -oblong, transparent, obtuse, 5-10 

 mm. broad, 3 -nerved, wavy and crisped on the edges ; fruits smooth or crenulate at 

 the back, with a rather acute beak almost as long as the fruit. 



Murray, Onkaparinga, and other streams ; an obstructive weed in the Torrens Lake 

 (Adelaide). Oct. -Feb. A cosmopolitan plant. 



2. P. ochreatus, Raoul. Leaves linear, obtuse, 2-4 mm. broad, with a broad central 

 nerve and usually 2 others near each margin ; fruits rather broad, rounded and smooth 

 or crenulate on the back, with a short, usually curved beak. — P. obtusifolius, F. v. M. 

 not of Mertens and Koch. 



Southern districts and Kangaroo Island. Nov. -Dec. 



