olisthi´um (ὄλισθος, slip), a succession in a landslip.
ombrometer (ὄμβρος, a rainstorm), a rain gauge.
-on (-ών, locative suffix), suffix used to denote a family.
oncospore (ὄγκος, hook), a plant with hooked disseminules.
orgadi´um (ὀργάς, άδος, meadowland partially wooded), an open woodland formation; orgadad, an open woodland plant.
orophyti´um (ὄρος, mountain), a subalpine plant formation.
oxodi´um (ὀξώδης, sour), a humus marsh formation; oxodad, a plant of a humus marsh.
pagi´um (πάγος, rocky hill, glacier), a succession in a glacial soil; pagophyti´um, a foot-hill plant formation.
pediophyti´um (πεδίον, plain), an upland plant formation.
pelagi´um (πέλαγος, surface of the sea), a surface sea formation; pelagad, a plant of the sea surface.