Areoles and spines
New plates with panel explanations and references to the literature.
Schematic illustrations from the supplied materials. Captions identify the scope of simplifications and any inaccuracies. Clicking an image opens it at full size.
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Areole and spine development
The left panel shows the positions of radial and central spines. The central panel connects the areole with stem tissues, and the right panel shows the elongated, hard cells of a mature spine. An areole is a short shoot that also produces hairs and other structures. [Mauseth 2006] [Silva et al. 2020]
The information about absence of xylem and phloem concerns ordinary spines. Specialised secretory glochids described in two species have a vascularised base and are shown on a separate plate.
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Opuntia glochidium
The large panel at left indicates the position of glochids in an areole. The central panel shows a single glochid with barbs pointing towards its base. At right are enlarged views of a bundle, the shaft surface and the base. [Robinson 1974]
The drawing is a schematic enlargement without a measurement scale. Base shape and the arrangement of surface cells are not identical in all opuntioids.
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Spine structure, distribution and types
The upper panels compare views of an areole, a single spine and its cross-section. Below are differences in spine shape and distribution within an areole. The terms “central” and “radial” describe position, while “hooked” and “flattened” describe shape. [Mauseth 2006] [Robinson 1974]
Categories may occur together on one plant. The plate is not a key for identifying species, and the cross-section proportions are schematic.
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Spines. Structure and possible functions
Panels 1–3 organise spine structure and descriptive traits. Panel 4 compares possible protective functions and effects on the environment around the stem surface. Panel 5 illustrates the developmental relationship between spines and leaves. [Mauseth 2006] [Robinson 1974] [Ju et al. 2012]
The arrow from leaf to spine indicates homology, not transformation of a mature leaf on a particular plant. The 100 μm scale bar is part of the drawing, with no measurement material specified. Spine effects on water and microclimate depend on species and conditions.
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Secretory glochids
The left side compares structures in Brasiliopuntia brasiliensis and Nopalea cochenillifera, accepted in the atlas as Opuntia cochenillifera. The right side distinguishes the expanded, vascularised base, unlignified middle part and tip. The drop at the tip indicates secreted nectar. [Silva et al. 2020]
The plate concerns specialised structures in two species studied. It does not show the structure of all glochids or ordinary spines. It is an educational reconstruction, not a microscopic image from a publication.
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Structures developing in an areole
An areole is a strongly shortened lateral shoot. The plate compares a young areole, spine formation, flower bud development and an areole with mature spines. The panels help distinguish structures but do not define a mandatory order of appearance. In some cacti, a period of meristem dormancy separates spine formation from flowering. [Mauseth 2006]
The label “meristem” refers to the formative tissue, not the whole visible areole cushion. The 5 mm scale bar is not linked to an identified species or a measurement. The figure does not document an experiment or development time.
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