Ferns in Suffolk

Page 1

FERNS IN

SUFFOLK

T h e ferns, or Filicinae, belong to the ancient plant order of Pteridophyta, classes of which have survived from Palaeozoic times. Unlike the flowering plant, the adult fern produces no seeds as s u c h ; instead, thousands of minute, one-celled spores form inside spore-cases—sporangia. T h e life history of the ferns has two distinct phases. It begins with the liberation of the spores from the sporangia Clusters, or sori. Given conditions of warmth and sustained dampness, the wall of the spore splits, and the cell develops into a flat, green, heart-shaped body called prothallus, which contains Chlorophyll and which is an individual plant. It is on the underside of these prothalli that are formed the male and female gametes—the antheridia and the archegonia—which correspond to the anthers and style of the flowering plant*. T h e first phase of the life history—the gametophyte—ends with the fusing of the two organs to form a Zygote. T h e second stage—the sporophyte—begins with the Zygote and culminates in the production of the spores by the adult fern. As soon as the Zygote is formed, the fronds proper appear, the first being very simple, but subsequent ones becoming rapidly more complex until the adult fern is attained. Some young ferns, for example the Male Fern (Dryopteris filix-mas), take only two seasons to become identifiable, but others, with bi- or tri-pinnate fronds are slower and often cause trouble in identification until they are mature, when the arrangement and type of sorus with its covering, or indusium, can be examined. In the British Isles there are six families of Filicinae, comprising some forty-five species. This number, however, is not conclusive as there is still doubt as to the specific or sub-specific status of some ferns. Suffolk is not generally regarded as fern country, as the relatively dry climate makes suitable habitats scarce. However, the country possesses about half the ferns on the British list. T w o species of the family Ophioglossaceae are to be found in Suffolk, the Adder's Tongue (Ophioglossum vulgatum) and the Moonwort (Botrychium lunaria). These two plants are often passed by, unnoticed beneath higher Vegetation, and even if discovered are frequently not recognised as ferns at all. T h e Adder's Tongue consists of a single, ovate, plantain-like, barren frond, with the simple, fertile, spike branching out from the top of the stalk. T h e Moonwort, also, has one barren frond although it bears its sporangia on a bi-pinnate stalk. T h e barren frond is divided into fleshy, fan-shaped pinnae. This fern is said to * T h i s is the general form of prothallus. Exceptions among Suffolk ferns are the Ophioglossaceae, whose prothalli are subterranean, and Azolla filiculoides which produces separate male and female prothalli from microspores and megaspores respectively.


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