COMMELINACEAE (SPIDERWORT FAMILY) 107 



fruit symmetrical, subturbinate : seed with a prominent protruding hilum, 

 deeply and unequally 12-15-ribbed: ovule 1. Cosmopolitan; lakes and stag- 

 nant ponds. 



6. Lemna gibba L. Sp. PL 970. 1753. Thallus unsymmetrical, obovate or 

 short-ob ovate, 2-6 mm. long, thickish or more or less strongly gibbous be- 

 neath, short-stalked when young, soon separating, provided with stomata 

 which are sparse beneath, obscurely 3-5-nerved: root-cap mostly short- 

 pointed, cylindrical, rarely long-pointed or obtuse: fruit symmetrical: seed 

 thick, deeply and unequally ribbed. World- wide in distribution. 



2. SPIRODELA Schleiden. GREATER DUCKWEED 



Anther-cells bilocellate by a vertical partition and longitudinally dehiscent. 

 Ovules 2. Thallus 7-11-nerved or more; rootlets several, with axile vascular 

 tissue. Otherwise as Lemna. 



1. Spirodela polyrhiza (L.) Schleid. Linnaea 13: 392. 1839. Thallus 2-10 

 mm. long, thick, flat and dark green above, slightly convex and purple be- 

 neath, palmately 5-15-nerved, bearing a central cluster of from 4-16 elongated 

 roots: root-cap pointed. In still water; widely distributed and occurring oc- 

 casionally in our range. 



19. COMMELINACEAE Reichenb. SPIDERWORT FAMILY 



Herbs, with fibrous or sometimes thickened roots, jointed and often branch- 

 ing leafy stems, and chiefly perfect and 6-androus, often irregular flowers, with 

 the perianth free from the 2-3-celled ovary, and having a distinct calyx and 

 corolla of 3 persistent sepals and as many ephemeral or deciduous (in ours 

 blue) petals. Style 1; stigma undivided. Pod 3 to several-seeded. Leaves 

 ovate, lanceolate, or linear, parallel- veined, flat, sheathed at the base; the 

 uppermost often forming a kind of spathe. 



Flowers irregular; 3 of the 6 stamens anther-bearing * . . .1. Commelina. 

 Flowers regular; stamens all anther-bearing . . . . . .2. Tradescantia. 



1. COMMELINA L. DAY FLOWER 



Stems branching, often procumbent and rooting at the joints. Floral leaf 

 heart-shaped and clasping, folded together or hooded, forming a spathe in- 

 closing the flowers, which expand for a single morning and are recurved on 

 their pedicels before and afterwards. Sepals somewhat colored, unequal; the 

 two lateral partly united by their contiguous margins. Two lateral petals 

 rounded, on long claws, the old one smaller. Sterile stamens with imperfect 

 cross-shaped anthers. 



1. Commelina crispa Wooton, Bull. Torr. Bot. Club 25: 451. 1898. Stems 

 slender, erect, or reclined and rooting towards the base: leaves oblong or linear- 

 lanceolate : spathes peduncled, conduplicate, orbicular-cordate when expanded, 

 in fruit somewhat hood-like. Commelina virginica. Colorado and southwest- 

 ward. 



2. TRADESCANTIA L. SPIDERWORT 



Freely branched; filaments folded: ovary pubescent in rib-like lines . 1. T. laramiensis. 

 Simple; filaments straight; ovary pubescent at apex . . . . 2. T. occidentals. 



1. Tradescantia laramiensis L. N. Goodding, Bot. Gaz. 33: 68. 1902. 

 Stems glabrous, freely branched, 3-4 dm. high: leaves widely spreading, 

 linear; the radical 5-10 mm. wide; the cauline narrower; the involucral only 

 2-3 mm. wide and very long: umbels sessile, terminating stems and branches: 

 flowers numerous, often as many as 50 in each umbel, pendent in age; pedicels 



