Nomenclatural synonyms

Nomenclatural synonyms [Taxonomy ]	Dictionary of botanic terminology index of names
Synonyms: Homotypic synonyms

Homotypic or nomenclatural synonyms are synonyms that come about when a name is nomenclaturally incorrect or sometimes when a species is moved from one genus to another.

Synonymy: why plants can have more than one valid name
Although each species is meant to have only one name under our system of nomenclatural rules, there are often several names that are applied under different circumstances. This is because some of them are to be applied following different classification systems, for example when different genera are recognized. Others are only applied when a narrow concept of the species is applied, falling into synonymy if the smaller species are lumped together into larger species, for which fewer names are required.
These names that can all apply to the same plant or group of plants are called synonyms, and there are different kinds of synonym:

The basionym
The nomenclatural synonym (homotypic synonyms)
The taxonomic synonym (heterotypic synonyms )

Homotypic or nomenclatural synonyms: (Names belonging to the same type)
Each species recognized can only have one correct name within a particular genus. Homotypic synonyms come about when a name is nomenclaturally incorrect or sometimes when a species is moved from one genus to another. Homotypic synonyms have a single (set of) type(s). One name is valid; other name(s) are invalid with reference to that type lot. Homotypic synonyms concerns names or combinations

Heterotypic or taxonomic synonyms: (Names belonging to the same taxon)
Heteroytpic synonyms are synonyms that refer to different types with which different names are associated, but which the scientist concerned considers to be the same taxon but different type
Heterotypic synonyms reflect a scientific opinion about distinctness of (terminal) taxa. Heterotypic synonyms always have different sets of types. One of the taxa is the currently accepted taxon.. Heterotypic synonyms concerns most often taxa at the terminal or subterminal levels

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Holdfast roots [ Botany ]
Dictionary of botanic terminology - index of names

Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.

Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans), develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994