606 



DIAPENSIACE/E. 



[Perigynous Exogens. 



any visible veins. Flowers solitary, terminal 



ccccx. 



Order CCXXXIII. DIAPENSIACE/E.— Diapknsiads. 



Diapensiacea, Link Handb. 1. 595. (1829) ; a § of Convolvulaceae ; Ed. pr. No. clxxvii. (1836) ; Endl. 



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



Diagnosis.— Gentianal Exogens, with no stipules, simple stigmas at the end of a manifest 

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



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



Calyx composed of 5 sepals which form 

 a broken whorl, are rather unequal, 

 and much imbricated ; scarcely dis- 

 tinguishable from the bracts which 

 are closely imbricated round 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, with 

 a broad connective, bursting trans- 

 versely ; in Pyxidanthera awned on 

 the lower valve. Disk 0. Ovary 

 superior, 3-celled ; each placenta with 

 7 ovules in Pyxidanthera, with an 

 indefinite number in Diapensia ; style 

 single, continuous with the ovary ; 

 stigma sessile, with 3 very short de- 

 current lobes. Capsule membranous 

 or papery, surrounded with the permanent sepals, terminated by the rigid style or 

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

 a slender radicle and two very short cotyledons, lying across the hilum 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 generally supposed 

 that this profound Botanist intended to refer Diapensia to the former spurious 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 with it of Diapensiads. The chief resemblances consist 

 in Diapensia having the filaments petaloid, and originating not from within the corolla 

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

 five of the divisions being broad and coloured, and the other five much narrower, and 

 shorter, colourless, and having anthers ; and in the embryo being filiform, slightly 

 2-lobed at one end. But both Diapensia and Pyxidanthera disagree with Hydrophyls 

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

 the anthers bursting transversely, and with a very broad connective ; in having 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 Diapensiacese originated with Link, yet that 

 author in placing it among Bindweeds was obviously unacquainted with its real structure, 

 and in assigning it for a character " semina membrana inclusa," 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. 

 Hydroph yllacea. 

 Position. — Loganiacese. — Djapensiace^e. — Stilbacese. 



Fig. CCCCX.— Pyxidanthera barhulata. 1. corolla cut open ; 2. perpendicular section of the ovary; 

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



