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ARCHICHLAMYDEAE 
Class i. ARCHICHLAMYDEAE 
Archichlamydeae Engler Syll. 92 (1892) including Chalazogamae p. 64 ; in Engler und Prantl Pflanzenfam. 
achtr. 344 (1897); Ascherson und Graebner Syn. iv, 2 (1908). 
The class Archichlamydeae includes the Polypetalae and the Monochlamydeae of De Candolle {op. cit.) and of 
Bentham and Hooker {op. cit.). The earlier orders of Archichlamydeae include those forms which we regard as 
primitively monochlamydeous, whilst those forms whose monochlamydeous perianth is thought to be due to suppres- 
sion of a corolla are placed later on in the class near the dichlamydeous forms from which they are believed to have 
descended. As what we believe to be primitively monochlamydeous forms occur throughout the subclasses 
Amentiflorae and Petalo'idae and also in the lower families of the subclass Centrospermae and the lower genera of the 
subclass Heterochlamydeae , and as forms which are monochlamydeous by reduction are found scattered throughout 
the higher Centrospermae and Heterochlamydeae and even the Metaclilamydeae , it is unwise to retain the group 
Monochlamydeae. 
Engler still divides the Archichlamydeae into two main groups, the first of which contains only the non-British 
family Casuarinaceae. We do not adopt these two groups, as we believe that the Casuarinaceae are best left near the 
Fagaceae where Eichler {Syll. der Vorlesungen 20 (1876)) and formerly Engler himself {Pflanzenfam. iii, pt. i, 16 
(1889)) placed them, as the peculiar characters on which the change was made have since been discovered in other 
genera of the Fagales. We have elsewhere {New Phytol. xi, 209(1912)) stated our reasons more fully for differing with 
Engler on this matter. 
We think it probable that the four sub-classes of the Archichlamydeae have descended from an unknown 
group of “ primitive angiosperms,” and have developed along diverging paths. 
For characters, see page 1. 
Subclasses of Archichlamydeae 
Subclass 1. Amentiflorae (p. 3). Usually trees or shrubs, less often perennial or annual 
herbs. Inflorescence usually a simple or compound catkin, less often a compound cyme or raceme ; 
ultimate branches of the compound inflorescences usually cymose. Flowers usually dioecious, or 
monoecious and diclinous, less often monoclinous. Perianth monochlamydeous, sepaloid, small or 
minute, rarely absent. Pollination usually anemophilous, rarely entomophilous. Ovary syncarpous. 
Fertilisation porogamous, mesogamous, or chalazogamous. Integument of seed double or single. 
Non-catkinate inflorescences occur, chiefly in the order Urticales. Exceptionally, monoclinous flowers may occur 
in any of the genera of this subclass, e.g., Populus, Salix, Castanea. Salix and Castanea are entomophilous. Meso- 
gamous fertilisation has been observed in Ulmus, and chalazogamous fertilisation in Juglans , in most of the genera 
of the order Fagales , and in Ulmus. 
Subclass 2. Petalo'ideae. Trees, shrubs, or herbs. Inflorescence compound, usually cymose 
or cymose-spicate ; ultimate branches usually cymose, rarely solitary. Flowers usually monoclinous, 
rarely diclinous, actinomorphic or zygomorphic. - Perianth usually monochlamydeous and petaloid, 
rarely monochlamydeous and sepaloid, rarely dichlamydeous and sepaloid. Pollination anemophilous 
or entomophilous. Ovary syncarpous. Fertilisation porogamous. Integument of seed double or 
absent. 
The suborder Loranthineae , including Viscum, has a sepaloid perianth. The perianth of Rumex and Rheum 
is dichlamydeous, and that of Rumex is also sepaloid. 
Subclass 3. Centrospermae. Inflorescence compound, cymose, cymose-spicate, or racemose, 
rarely simple and spicate ; ultimate branches of the compound inflorescences usually cymose, or very 
rarely reduced to a single flower. Flowers usually monoclinous, rarely diclinous. Perianth usually 
present, monochlamydeous in the earlier orders, usually dichlamydeous in the later ones ; usually 
actinomorphic, very rarely zygomorphic. Pollination anemophilous in the earlier orders, usually 
entomophilous in the later ones, autophilous in the reduced achlamydeous forms. Stamens usually 
hypogynous, usually as many as the sepals and antisepalous in the earlier families, usually hypogynous 
and obdiplostemonous in the later ones, rarely perigynous, very rarely some petaloid. Ovary usually 
syncarpous, or with only 1 carpel, rarely apocarpous, usually superior, rarely subinferior. Placentation 
basal in the earlier orders, free-central in some of the later ones, rarely axile or parietal. Fertilisa- 
tion porogamous. Embryo curved, very rarely straight. Integument of seed double. 
In the forms with a simple and spicate inflorescence (e.g., Salicornia disarticulata), each of the ultimate branches 
of the inflorescence has lost all but the central flower. The pistillate flowers of most species of A triplex are achlamy- 
deous. Apetalous forms occur in the Dianthaceae (e.g., in some forms of Cerastium and Stellaria) : it is clear that 
the apetaly is here due to reduction, as closely allied forms are dichlamydeous. The perianth of Montia is zygo- 
morphic. In Mesembryanthemum, the outer stamens are petaloid ; and the placentation at maturity is parietal. 
Hemi-epigynous flowers occur in Beta, Mesembryanthemum , and Portulaca. The embryo is straight in Dianthus. 
