ISSN:
1615-6110
Keywords:
Pteridophyta
;
Hypolepidaceae
;
Dennstaedtiaceae
;
Pteridium
;
Histiopteris
;
Hypolepis
;
Dennstaedtia
;
Construction morphology
;
leaf development
;
phase differentiation in leaf development
;
soral development
;
sorus
;
receptacle
;
indusium
;
basipetal marginal sorus
;
phylogeny
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract In contrast to the generally favoured hypothesis that the marginal position of sporangia and sori is the primitive condition, Hagemann (e.g. 1984a) holds the view that the superficial position of reproductive organs is primitive. Marginal reproductive organs correlate with a distinct succession of a vegetative and a reproductive developmental phase in the sporophyll (“phase differentiation in leaf development”). Since phase differentiation means an increase in complexity, marginal reproductive organs are considered advanced. In order to examine the relations between submarginal and marginal sori in the light of Hagemann's hypothesis, various soral forms of ferns were analysed using the methodological framework of construction morphology sensu Weber (1958). The sorus is regarded as a reproductive region of the leaf surface that comprises not only the sporangia but also the receptacle as an essential component. The growth pattern of the receptacle, the developmental succession of the sporangia, and the formation of the indusia lead to the recognition of several sorus types. In the present paper the “basipetal marginal sorus” is presented and defined as the combination of (a) a ridge-, cushion-, or rod-shaped receptacle, (b) a basipetal sequence of sporangia initiation, and (c) the presence of a lower and an upper indusium or of a cup-shaped indusium. As the first examples of this type, the sori of selected Hypolepidaceae and Dennstaedtiaceae are treated in detail. Regarding the phylogenetic relationships of the present families, the following conclusions can be drawn: (1) Owing to the meristem fusion of the indusia the sorus ofDennstaedtia possesses a new quality as compared to that of the Hypolepidaceae. Therefore, the Hypolepidaceae and the Dennstaedtiaceae should not be combined in a single family, as suggested by some authors. (2) The marginal position of the sori, and, in addition, the highly complex soral construction of the Dennstaedtiaceae, are not in support of the primitiveness of the two families, as sometimes assumed. (3) A sorus construction as found inDennstaedtia glauca can be gradually derived from a less elaborate one, such as that found, e.g., inPteridium. The continuous increase in the perfection of the soral construction (Pteridium → Dennstaedtia) suggests a placement of the Dennstaedtiaceae after the Hypolepidaceae.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00985044
Permalink
