RHODOTYPOS 
559 
u sp. Eur., Medit.; 2 in Brit, (yellow-rattle), common in damp 
pastures. Semi-parasites with loose pollen firs, (see order). 
Rliipsalis Gaertn. Cactaceae (1. 3). 50 sp. trop. Am., Madag., Ceylon 
(see order). Epiphytes, rarely thorny, sometimes of Cereus-like 
structure, sometimes Phyllocactus-like, or with cylindrical stems 
(compare sp. of Euphorbia). Fruit fleshy. 
Rliizotoleae = Caryocaraceae. 
Rhizophora Linn. Rhizophoraceae. 3 sp., R. Mangle L. in Am., 
R. mucronata Lam. and another, Japan to E. Afr. These mangroves 
(p. 19 1) are moderate-sized trees with a great development of roots 
from the stem and branches. On the sub-aerial parts of the roots are 
large lenticels, probably serving in the same way as the aerenchyma 
of Bruguiera &c. The seed germinates upon the tree, the hypocotyl 
projects at the micropyle and grows rapidly. The bark is used for 
tanning, yielding a substance known as cutch (cf. Acacia). 
Rhizophoraceae. Dicotyledons (Archichl. Myrtiflorae). 12 gen. with 
50 sp. trop., mostly Old World. The general habit of the mangroves 
is described on p. 188. They are trees with opp. stip. leaves; firs, 
solitary or in cymes &c., $ , hypo- to epi-gynous. K usually 4 — 8; 
C 4 — 8 ; A 8 — 00 , inserted on outer edge of perigynous or epigynous 
disc; G (2 — 5), 2 — 5-loc. with usually 2 anatropous pendulous ovules 
in each loc. Fruit a slightly soft berry. Chief genera : Rhizophora, 
Bruguiera. Placed in Myrtales by Benth. -Hooker, in Myrtiflorae by 
Warming. 
Rhodea Endl. = Rohdea Roth. 
Rhodochiton Zucc. Scrophulariaceae (11. 5). 1 sp. Mexico, R. volu- 
bile Zucc., a favourite greenhouse twiner with sensitive petioles (cf. 
Clematis). 
Rhododendron Linn. (incl. Azalea Linn., q.v.). Ericaceae (1. 2). 200 sp. 
“ One sp. (R. Lochae F. Muell.) is found in trop. Austral., the greatest 
richness of sp. is in E. Asia, from S. China to the Himalaya and 
Japan; a second and lesser abundance is found in temp. N. Am., 
and a few sp. in the arctic regions. 4 sp. in Mid. and S. Eur., 5 in 
Caucasus. The alpine sp. are called ‘alpine roses. (Drude.) Many 
sp. and hybrids are cultivated. They are shrubs and small trees with 
leathery leaves ; the leaves of § Azalea last one year, those of the other 
subgenera usually more. Large winter buds are formed covered with 
scale leaves; the larger and stouter ones contain infls., the slender 
ones merely leaves. The branch bearing an infl. is continued by the 
formation of a bud in one of the upper leaf axils. Some of the Indian 
sp. are epiphytic. The corolla is slightly zygomorphic, and the sta. 
and style bend upwards to touch the under surface of a visiting insect. 
R. ferrugineum L., the alpine rose, is protandrous and visited by 
humble-bees. 
Rliodotypos Sieb. et Zucc. Rosaceae (ill. 5). R. kerrioides S. et Z., 
the only sp. (Japan), is a favourite garden shrub. It has opp. leaves, 
