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Onoclea sensibilis, the sensitive fern, also known as the bead fern, is a coarse-textured, medium to large-sized deciduous perennial fern. The name comes from its sensitivity to frost, the fronds dying quickly when first touched by it. It is sometimes treated as the only species in Onoclea, [2] but some authors do not consider the genus ...
The fertile leaves appear first; their green color slowly becomes brown as the season progresses and the spores are dropped. The spore-bearing stems persist after the sterile fronds are killed by frost, until the next season. The spores must develop within a few weeks or fail. The Osmundastrum cinnamomeum fern forms huge clonal colonies in ...
Fern spores are borne in sporangia which are usually clustered to form sori. The sporangia may be covered with a protective coating called an indusium. The arrangement of the sporangia is important in classification. [6] In monomorphic ferns, the fertile and sterile leaves look morphologically the same, and both are able to photosynthesize.
The false indusia look similar, though not identical, to the rest of the leaf tissue, and are 0.05–0.25 mm wide. Beneath them, the sori do not form long lines, but are discontinuous and concentrated on lobes at the tip and sides of the pinnule. Each sporangium in a sorus carries 64 spores. The diploid sporophyte has a chromosome number of 60.
The name "walking fern" derives from the fact that new plantlets grow wherever the arching leaves of the parent touch the ground, creating a walking effect. Both have evergreen, undivided, slightly leathery leaves that are triangular and taper to a thin point. On the bottom of the leaves, sori, or spore-bearing structures, cluster along the veins.
The gametes fuse, forming the diploid sporophyte, the 'fern' part of the life cycle. [8] [10] [11] Aglaomorpha also naturally exhibits apospory, the production of a gametophyte not from spores, but directly from the vegetative cells of the sporophytes. Their leaves can develop prothalli under dim light and sporophytic buds in strong light. [12]
[4] [5] "Frond" is commonly used to identify a large, compound leaf, but if the term is used botanically to refer to the leaves of ferns and algae it may be applied to smaller and undivided leaves. Fronds have particular terms describing their components. Like all leaves, fronds usually have a stalk connecting them to the main stem.
An annulus in botany is for ferns an arc or a ring of specialized cells on the sporangium. These cells are arranged in a single row, and are associated with the release or dispersal of spores. In mosses it is a ring of cells around the tip of the sporangium. In flowers it is a ring of hairs within the flower tube.