606 



DIAPENSIACE^. 



[Perigynous Exooens. 



Order CCXXXIII. DIAPENSIACEiE.— Diapensiads. 



Diapensiacea, Link Handb. 1. 595. (1829) ; a § of ConvolyiQacese ; Ed. pr. No. clxx^^i. Q836) ; Endl. 

 Gen. p. 760, ; Meisner Gen. p. 272. 



Diagnosis. — Gentianal Exogeiis, loith no stipules, simple stigmas at the end of a manifest 

 style, axile placentce, indefinite peltate seeds, and interpetalous stamens. 



Prostrate under-shrubs, with small densely imbricated leaves wliicli have scarcely 

 any visible veins. Flowers solitary, tennmal. Calyx composed of 5 sepals which form 



a broken whorl, are rather miequal, 

 and much imbricated ; scarcely dis- 

 tinguishable from the bracts which 

 are closely imbricated romid it. Co- 

 rolla monopetalous, regular, with an 

 imbricated aestivation. Stamens 5, 

 equal ; the filaments petaloid and 

 arising from the margin of the sinus 

 of the corolla ; anthers 2-celled, ^^•ith 

 a broad connective, bursting trans- 

 versely ; hi Pyxidanthera awiied on 

 the lower valve. Disk 0. Ovary 

 superior, 3-celled ; each placenta with 

 7 ovules in Pyxidanthera, with an 

 mdefinite number in Diapensia ; style 

 single, continuous with the ovary ; 

 2 Fig. CCCCX. stigma sessile, with 3 very short de- 



current lobes. Capsule membranous 

 or papery, smToimded with the pei*manent sepals, terminated by the rigid style or 

 its base. Seeds with a brittle deeply pitted skin, peltate. Embryo very small, with 

 a slender radicle and two very short cotyledons, Ijmg across the liilum in a mass of 

 fleshy albumen. 



From the manner in which Diapensia was associated by Brown (Prodromus, 482), when 

 he separated it along with Hydroleacese from Bindweeds, it has been geuei'ally supposed 

 that this profound Botanist intended to refer Diapensia to the former spmnous Order. 

 But Diapensia is in reality nearer Phloxworts than Hydroleacese, and yet more nearly 

 allied by its small embryo and copious albumen to Hollyworts and Loganiads. Hydro- 

 leacese themselves must merge in Hydrophyls, and the free central placentation of that 

 Order forbids the association mth it of Diapensiads. The chief resemblances consist 

 m Diapensia ha%'uig the filaments petaloid, and originating not from within the corolla 

 but from the margin of the sinuses, so that the coroUa might be described as 1 0-cleft, 

 five of the di^-isions being broad and coloured, and the other five much narrower, and 

 shorter, colourless, and ha^•ing anthers ; and in the embryo beuig filiform, shghtly 

 2-lol)ed at one end. But both Diapensia and Pyxidanthera disagree with Hydrophyls 

 in havhig a calyx consisting of five unequal sepals forming a broken whorl ; in having 

 the anthers bm'stmg transversely, and Arith a very broad connective ; in ha^ing only 

 one style instead of two ; in being destitute of an hypogynous disk ; and finally, in 

 the embryo lying in the midst of fleshy albumen across the hilum. At least this is 

 certainly the case in Pyxidanthera, and I have no reason to doubt its being equally 

 the case with Diapensia. 



Let me add, that although the name of Diapensiaceae originated with Link, yet that 

 author in placing it among Bindweeds was obN-iously unacquainted with its real structm'e, 

 and in assignmg it for a character " semina membrana inclu.sa," seems to have assumed 

 that in this respect it agrees with Hydrophyls, which is not the fact. 



The species are mountain plants of the north of Europe and North America. 

 They are not known to possess any useful properties. 



GENERA. 



Diapensia, L. | Pyxidanthera, Michx. 



Numbers. Gen. 2. Sp. 2. 

 HydrophyllacecB. 

 Position. — Loganiacese. — Diapensiace.e. — Stilbacese. 



Fig. CCCCX.— Pyxidanthera barbulata. 1. coroUa cut open ; 2. perpendicular section of the ovary ; 

 3. anther; 4. seed; 5. embryo. 



