502 



POLYGONACE^, 



[Hypogynous Exogens. 



Order CXCI. POL YGONACE^.— Buckwheats. 



Polygcmeae, Juss. Gen. 82. (1789) j R. Brown, Prodr. 418. (1810) ; Bentham in Linn. Trans. (1836): 

 Endl. Gen. ciii.— Polygonaceae, Ed. pr. (1836); Meisncr Gen. 316. 



Diagnosis. — Silcnal Exogens, with no corolla, cmd a calyx usually coloured, an orthotropal 

 ovule, and a usually triangular nut. 



Herbaceous plants, rarely shrubs. Leaves alternate, their stipules cohering round 

 the stem in the foi-m of an ochrea ; when young, rolled backwards, occasionally wanting. 



Fig. CCCXLIV. 



Flowers occasionally unisexual, often in racemes. Calyx 

 free, often coloured, imbricated in sestivation. Stamens 

 very rarely perigjTious, usually definite and inserted in the 

 bottom of the calyx ; anthers dehiscing lengthwise. Ovary 

 free, usually formed by the adhesion of 3 carpels, one-celled, 

 with a single erect o^^lle, whose foi*amen always points up- 

 wards ; styles or stigmas as many as the carpels of which 

 the ovary consists ; ovule orthotropal. Nut usually trian- 

 gular, naked, or protected by the calyx. Seed with farina- 

 ceous albumen, rarely with scarcely any ; embryo inverted, 

 generally on one side, sometimes in the axis ; radicle supe- 

 rior, long. 



Brown remarks, that " the erect ovulum with a superior 

 radicle together afford the most important mark of distinction between Polygonaceae 

 and Chenopodiacese, a character which obtains even in the genus Eriogonum, in which 

 there is no petiolar sheath, and scarcely any albumen, the Httle that exists bemg fleshy ;" 

 to which may be added, that theu' orthotropal ovule divides them from all the other 

 Orders of the Silenal AUiance. Generally speaking, however, the cohesion of the 

 scarious stipules into a sheath, technically called an oclu'ea, or boot, is sufficient to 

 distingTiish Buckwheats from the neighbouring Orders. Then* aflfinity, moreover, does 

 not appear to be so close with Chenopods as \\ith Cloveworts, for they have the very 

 important peculiarity that their ovary is formed by the consoHdation of 3 carpellaiy 

 leaves touching each other in a valvate manner, and thus producing a triangular form 

 in the ripe fruit ; and if even this is departed from, yet the ovary is midoubtedly com- 

 pound and not simple as in Chenopods. Bentham admits two tribes, Polygoneae, wliich 

 have loose flowers and ochreate stipules, and Eriogonese which have flowei's in involu- 

 cres and usually no stipules. The latter bring them near Nyctagos. 



Fig. CCCXLIV. — Polygonum lapathifolium. 1. a flower cut open ; 2. a vertical section of the seed : 

 3. a flower of P. Convolvuli ; 4. a transverse section of a seed ; 5. a diagram of the flower of Rumex 

 crispus ; 6. a vertical section of its ripe fruit, &c, ; 7. its fruit. 



