Cataphyll -- "Brown or colorless scale-like structures believed to be modified leaves." (Plant Identification Terminology, Harris & Harris, 2nd edition, p. 22) For the special case of Trillium - structures that protect the apical buds of the rhizome.
Clump -- Two or more stems arising from one rhizome, divided into Apical clump - stems arising from the rhizome apex; and Lateral clump - stems arising from rhizome offsets. Definitions proposed by John Gyer.
Cluster -- A group of stems arising from a closely spaced group of rhizomes that arise from seeds dropped and germinated near the mother plant. Definitions proposed by John Gyer.
Elaiosome (elaios- oil, some- body) is a fleshy structure that is attached to the seeds of many plant species. From: Wikipedia. The attractants in the elaiosome induce ants or other animals to carry the seeds away, thus facilitating seed dispersal. In Trillium, seed dispersal induced by the elaiosome is probably carried out by ants and wasps.
Growth Phases -- In Trillium, growth is divided into skotomorphic and photomorphic phases. Together, the annual alternation between skotomorphic growth and photomorphic growth. Definitions proposed by John Gyer.
Growth Stages -- (see: Ohara, Plant Species Biology for the concept) The stages of annual plant development and enlargement between seed germination and sexual maturity. Definitions proposed by John Gyer.
Myrmecochorous -- Having the property in seeds of attracting and being dispersed by ants. From: Case & Case.
Pedicellate -- Having the flower carried above the peduncle on a stem called a pedicel.
Photomorphogenic -- Type of plant growth that uses and requires light as its energy source. In Trillium, the development or growth of green shoots above ground. Definitions proposed by John Gyer.
Sessile -- Having a flower or leaf born directly on the stem or peduncle rather than on an elongeated stalk. C.f. Petiole.
Skotomorphogenic -- Type of plant growth that uses stored energy reserves and does not directly require light to function. In Trillium, the underground growth processes that take place before the first leaf appears in seedlings or while the green shoots are absent in older plants. Definitions proposed by John Gyer.
Stem -- The above-ground stalk is properly referred to as a peduncle.
For definitions of more general terms from plant science, see the Glossary of Plant Biology.
For more on the genus Trillium: