502 



POLYGONACE^E. 



[Hyfogynous Exogens. 



Order CXCI. POLYGONACE^.— Buckwheats. 



Polvtrone* Juss. Gen. 82. (1789); R. Broton, Prodr. 418. (1810); Bentham, in Linn. Trans. (1836); 

 JB Endl. Gen. ciii.— Polygonacese, Ed. pr. (1836); Meaner Gen. 316. 



Diagnosis. Silcnal Exogem, with an orthotropal ovule, and a usually triangular nut. 



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

 the stem in the form of an ochrea ; when young, rolled backwards, occasionally wanting. 



Fig. CCCXL1V. 



Flowers occasionally unisexual, often in racemes. Calyx 

 free, often coloured, imbricated in aestivation. Stamens 

 very rarely perigynous, 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 ovule, whose foramen 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 Polygonacese 

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

 there is no petiolar sheath, and scarcely any albumen, the little that exists being fleshy ;' 

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

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

 scarious stipules into a sheath, technically called an ochrea, or boot, is sufficient to 

 distinguish Buckwheats from the neighbouring Orders. Their affinity, moreover, does 

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

 important peculiarity that their ovary is formed by the consolidation of 3 carpellary 

 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 undoubtedly com- 

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

 have loose flowers and ochreate stipules, and Eriogoneae which have flowers m involu- 

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



Fi» CCCXLIV —Polygonum lapathifolium. 1. n 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. 



