The structure and function of a leaf can be modified over the course of evolution as a plant adapts to a particular environment. Some leaves may be converted to storage structures below ground (as with a bulb) or into plant defense structures (as with a spine). When function of the leaf blade is no longer primarily photosynthesis, some other plant part is usually modified to take its place. A
phyllode
is a petiole that has become flat and photosynthetic, looking much like a leaf blade.
Figure \(\PageIndex{1}\): A diagram of leaf modifications. In each plant (A-D), one leaf has been shaded with orange. In A, the blade has been modified for a trap, the petiole is flattened into a phyllode. In B, the blade is a compound leaf and the petiole is flattened into a phyllode. In C, some of the leaves are tendrils (emerging below axillary buds). In D, the basal leaves are thick and fleshy with a short stem (a bulb). Diagram by Nikki Harris,
CC-BY 4.0
with labels and color added by Maria Morrow.
Bulb
Figure \(\PageIndex{2}\): The onion bulb has a relatively small stem (tan tissue just above the roots) surrounded by thick, fleshy leaves. Image by
JonRichfield
(
CC-BY-SA
).
Succulent
Figure \(\PageIndex{3}\): Succulent leaves are thickened for water storage. This water-storing tissue is called hydrenchyma (see Figure \(\PageIndex{4}\), bottom). Photo by Simon Burchell,
CC BY-SA 4.0
, via Wikimedia Commons.
Figure \(\PageIndex{4}\): Top: "(A) Plants of
Guzmania lingulata
in the field at La Selva biological Station, Costa Rica, and (B) a single leaf of
G. lingulata
labeled with the two leaf regions examined." Bottom: "Sections of leaves of
G. lingulata
used to measure anatomical traits. Leaf clearings of the leaf blade (A) and tank region (B) used to determine interveinal distance (Div; black arrow); scale bars in (A) and (B) = 500 μm. Cross-sections of the leaf blade (C) and tank region (D); red lines indicate pathways for water between vein and abaxial surface (red line in (C) used to calculate Dmes; black arrow indicates distance between vein and epidermis Depi); scale bars in (C) and (D) = 50 μm. Abbreviations: bundle sheath cells (bs), hydrenchyma (hyd), mesophyll (mes), stomate (sto), and trichome (tri)." Figures and caption text from
Leaf Hydraulic Conductance for a Tank Bromeliad: Axial and Radial Pathways for Moving and Conserving Water
, North et al. 2013.
Creative Commons Attribution 3.0 Unported
.
Tendril
Figure \(\PageIndex{5}\): Many plants in the bean family (Fabaceae) produce leaf tendrils where all or part of the leaf forms a tendril. The first image is an illustration of a plant with compound leaves, some of the leaflets forming tendrils. The second image is of
Vicia villosa
with the terminal leaflets forming three tendrils. First image from Elsie Garrett Rice, Public domain, via Wikimedia Commons. Second image from Harry Rose from South West Rocks, Australia,
CC BY 2.0
, via Wikimedia Commons.
Figure \(\PageIndex{6}\): "Leaf tendrils: In weak-stemmed plants, leaf or a part of leaf gets modified into tendrils i.e., a green coiled threadlike structure which helps in climbing around the support. Gloriosa or Glory Lily has leaf tip modified into tendrils." Image and caption text by Krishna satya 333,
CC BY-SA 4.0
, via Wikimedia Commons.
Spine
Figure \(\PageIndex{7}\): Cactus spines are not stems, but modified leaves. These spines have a thick cuticle and stomata can be seen as darker green areas within the pale white cuticle. Photo by André Karwath aka Aka,
CC BY-SA 2.5
, via Wikimedia Commons.
Figure \(\PageIndex{8}\): Ocotillo leaf petioles form into spines. Note the axillary buds present in the axil of each spine. Photographed by and copyright of (c) David Corby (
User:Miskatonic
, uploader) 2006. This file is licensed under the
Creative Commons
Attribution-Share Alike 3.0 Unported
license.
Figure \(\PageIndex{9}\): Stipular spines of an
Acacia
sp. The paired sharp armaments subtend the leaves on this woody shrub. Dr Mary Gillham Archive Project,
CC BY 2.0
, via Wikimedia Commons.