Zostera. | NAIADACES. 755 
The exact position of the New Zealand plant must remain doubtful until 
the fructification has been obtained, but it is probably the same as the Australian 
and Tasmanian Z. tasmanica, which seems hardly different from narrow-leaved 
forms of the northern Z. marina. 
OrpER LXXXIX. CENTROLEPIDEA£. 
Annual or perennial tufted often moss-like plants, of small size. 
Leaves linear or setaceous, either all radical or densely imbricated 
on the short stems and branches. Flowers very small, usually 
hermaphrodite, one or several within 1-3 bracts, forming little 
heads or spikelets terminating short scapes or peduncles. Brac- 
teoles or glumes under each flower 1-3, hyaline, sometimes want- 
ing. Perianth none. Stamens 1-2; filaments filiform; anthers 
versatile, 1-celled. Ovary either 1-celled, or with 2-3 collateral 
cells, or of 2 or more free or irregularly connate carpels superposed 
in 2 rows; ovules solitary and pendulous in each cell or carpel ; 
styles as many as the cells or carpeis; stigmas linear. Fruit 
small, dry, pericarp membranous, the cells or carpels opening 
extrorsely by a longitudinal slit. Seed pendulous or laterally 
affixed ; albumen farinaceous ; embryo minute. 
A small and inconspicuous order, comprising 4 or 5 genera and about 30 
species. With the exception of the New Zealand species, one found in China, 
and one in antarctic South America, the order is confined to Australia. It has 
no properties of importance. 
Flowers crowded in a terminal head surrounded by several 
bracts. Stamens and 1-celled ovaries irregularly mixed, 
without inner bracts by a ae .. 1. TRITHURIA. 
Flowers within 2 alternate bracts, 1-5 within each bract. 
Stamen 1. Ovary of 3 or more carpels superposed in 
2 rows (rarely reduced tol) .. ae Bt es 
Flowers with 2-3 alternate bracts, 1-2 within each bract. 
Stamens 2. Ovary of 2 collateral cells or carpels .. 8. GAIMARDIA. 
2. CENTROLEPIS. 
1, TRITHURIA, Hook. f. 
Minute tufted and stemless annual herbs. Leaves all radical, 
filiform. Secapes short, slender, terminating in several spreading 
bracts enclosing a head of minute flowers. Flowers numerous, 
densely crowded, each probably consisting of a single stamen and 
ovary, but the stamens and ovaries so closely placed as to appear 
irregularly mixed. Perianth wanting. Stamens with a filiform 
filament and oblong anther. Carpels 3-angled or compressed in 
the Australian species, not angled in the one found in New Zealand. 
Styles 2-3 or numerous. Fruiting carpels 2-3-angled in the Aus- 
tralian species, splitting from the base upwards into as many valves 
as angles. 
The genus also includes 2 species found in Australia. 
