232 Alexander W. Evans, 



Section I. Astromarchantia 



I. Marchantia polymorpha L, 

 Marchantia polymorpha L. Sp. Plant. 1603. 1753. 

 Marchantia sfellata Scop. Fl. Carn. 24 ed. 353. 1772. 

 Marchantia umhellata Scop. /. c. 354. 1772. 

 Marchantia coarctata Corda; Opiz, Beitr. zur Naturg. 647. 



1828 (nomen nudum). 

 Marchantia elliptica Corda, /. c. 647. 1828 {nomen nudum). 

 Marchantia Kablichiana Corda, /. c. 647. 1828 (nomen nudum). 

 Marchantia macrocephala Corda, /. c. 647. 1828. {nomen 



nudum) ; Sturm, Deutschl. Flora 2 : 63. pi. 17. 1832. 

 Marchantia vittata Raddi, Mem. Soc. Ital. Modena 20: 45. 1829. 

 Marchantia Syckorae Corda; Nees von Esenbeck, Naturg. 



Europ. Leberm. 4 : 97. 1838. 

 Marchantia oregonensis Staph. ; Roll, Bot. Centralbl. 43 : 203. 



1891. 



Thallus pale to dark green, not glaucous, sometimes with a 

 brownish or purplish median band on the upper surface, often 

 more or less pigmented with purple on the lower surface, usually 

 0.75-1.25 cm. wide and 4-6 cm. long, repeatedly dichotomous, 

 the successive forks usually 2 cm. or less apart; texture some- 

 times delicate, sometimes firm, but never leathery, margin entire 

 or minutely denticulate ; epidermis composed of cells with 

 thin or slightly thickened walls, mostly 20-60/x long (averag- 

 ing about 29/x) and 12-20/* wide (averaging about i6fi), 

 papillae present near the margin or absent altogether ; pores 

 (with their surrounding cells) mostly 60-75/* long and 40-60/* 

 wide, sometimes measuring as much as 90 x 65/*, surrounded 

 usually by four rows of cells (two in each series), each row being 

 usually composed of four cells, inner opening usually four-sided, 

 the sides rarely concave throughout, each bounding cell usually 

 projecting inward in the form of a rounded papilla with sub- 

 parallel or converging sides, mostly with a resinous deposit ; air- 

 chambers low, more or less elongated, their boundaries indistinct 

 when viewed through the epidermis, usually present everywhere 

 (except close to the margin) but sometimes absent from the 

 median region, rows of photosynthetic cells sometimes three cells 

 long but often shorter ; compact ventral tissue mostly twelve to 

 twenty cells thick in the median portion, destitute of slime cells 

 and sclerotic cells, the cell walls slightly thickened and showing 

 distinct pits ; ventral scales in three rows on each side of the 

 thallus, median and marginal scales in distinct rows, laminar 

 scales in a more indefinite row, scales often more or less pigmented 



