Phylloclades and cladodes are flattened, photosynthetic shoots, which are usually considered to be modified

branch A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' twig'' usually ...

es. The two terms are used either differently or interchangeably by different authors. '' Phyllocladus'', a genus of conifer, is named after these structures. Phylloclades/cladodes have been identified in fossils dating from as early as the

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Pale ...

Definition and morphology

The term "phylloclade" is from the

New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Literary Latin used in original, scholarly, and scientific works since about 1500. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy ...

''phyllocladium'', itself derived from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''phyllo'', leaf, and ''klados'', branch. Definitions of the terms "phylloclade" and "cladode" vary. All agree that they are flattened structures that are photosynthetic and resemble leaf-like branches. In one definition, phylloclades are a subset of cladodes, namely those that greatly resemble or perform the function of leaves, as in

Butcher's broom ''Ruscus aculeatus'', known as butcher's-broom, is a low evergreen dioecious Eurasian shrub, with flat shoots known as cladodes that give the appearance of stiff, spine-tipped leaves. Small greenish flowers appear in spring, and are borne singly ...

(''Ruscus aculeatus'') as well as '' Phyllanthus'' and some ''

Asparagus Asparagus, or garden asparagus, folk name sparrow grass, scientific name ''Asparagus officinalis'', is a perennial flowering plant species in the genus '' Asparagus''. Its young shoots are used as a spring vegetable. It was once classified ...

'' species. By an alternative definition, cladodes are distinguished by their limited growth and that they involve only one or two internodes. By this definition, some of the most leaf-like structures are cladodes, rather than phylloclades. By that definition, ''Phyllanthus'' has phylloclades, but ''Ruscus'' and ''Asparagus'' have cladodes. Another definition uses "phylloclade" to refer a portion of a leaf-like stem or branch with multiple nodes and internodes, and "cladode" for a single internode of a phylloclade. Although phylloclades are usually interpreted as modified branches, developmental studies have shown that they are intermediate between leaves and branches as their name indicates. Molecular genetic investigations have confirmed these findings. For example, Hirayama et al. (2007) showed that the phylloclade of ''Ruscus aculeata'' "is not homologous to either the shoot or the leaf, but that it has a double organ identity," which means that it combines shoot and leaf processes.

Similar structures

* Aristate leaves end in a stiff point that may continue the primary leaf vein; this can resemble the stem end of a phylloclade/cladode. * Epiphylly: flowers and fruit develop "on a leaf". A stem and a leaf are merged with one another. Examples include ''Monophyllaea'' in family '' Gesneriaceae'' and '' Helwingia'' in Helwingiaceae.

Illustrations

image:Illustration Ruscus aculeatus0.jpg, Botanical illustration of ''Ruscus aculeatus'' showing leaf-like phylloclades/cladodes image:RuscusPhylloclade.jpg, Phylloclade/cladode of ''Ruscus'' sp. showing the spine formed by the stem axis image:Starr 031114-0007 Asparagus asparagoides.jpg, Leaf-like cladodes/phylloclades of '' Asparagus asparagoides'' image:Helwingia japonica1.jpg, Epiphylly in '' Helwingia japonica'' for comparison

References

{{Commons category, Cladodes, Phylloclade Plant morphology Plant anatomy