Systematic studies in the genus Mohria ( Anemiaceae : Pteridophyta ) . III . Comparative sporangium and spore morphology

The genera Mohria and Anemia (Anemiaceae: Pteridophyta) can be separated on both their sporangia and spores. In Mohria the capsule is globose with an apical annulus but in Anemia it is ovate-globose to cylindrical with a subapical annulus. The spores of both genera are radially symmetrical, tetrahedral and trilete with near parallel muri. The exinal sculpture in Mohria is cicatricose and in Anemia it can be canaliculate or cicatricose. In both genera the mural sets anastomose to form common muri that extend from near the distal pole to the equatorial radial region. The muri in Mohria are hollow and differ from those in Anemia which are solid or microporate. Supramural sculpturing in Mohria and Anemia is perinous. Spores of the other schizaealean ferns show no or little taxonomic affinities with Mohria and Anemia. In Actinostachys and Schizaea the spores are monolete and in Lygodium trilete but the exinal sculpture is smooth.

The genera Mohria and Anemia (Anemiaceae: Pteridophyta) can be separated on both their sporangia and spores.In Mohria the capsule is globose with an apical annulus but in Anemia it is ovate-globose to cylindrical with a subapical annulus.The spores of both genera are radially symmetrical, tetrahedral and trilete with near parallel muri.The exinal sculpture in Mohria is cicatricose and in Anemia it can be canaliculate or cicatricose.In both genera the mural sets anastomose to form common muri that extend from near the distal pole to the equatorial radial region.The muri in Mohria are hollow and differ from those in Anemia which are solid or microporate.Supramural sculpturing in Mohria and Anemia is perinous.Spores of the other schizaealean ferns show no or little taxonomic affinities with Mohria and Anemia.In Actinostachys and Schizaea the spores are monolete and in Lygodium trilete but the exinal sculpture is smooth.

UITTREKSEL
Mohria en Anemia (Anemiaceae: Pteridophyta) kan onderskei word op grond van hul sporangiums en spore.By Mohria is die sporangiumkapsule bolrond met 'n apikale annulus, maar by Anemia is dit eiervormig-bolrond tot silindries met 'n subapikale annulus.Die spore van albei genusse is radiaal simmetries, tetrahedraal en trileet met feitlik parallelle muri.By Mohria is die eksien gelitteken, maar by Anemia kan dit gelitteken of gekanaliseerd wees.Die muri-stelle by albei genusse verenig om gemeenskaplike muri te vorm wat vanaf die distale pool tot by die ekwatoriaal radiale gebied strek.By Mohria is die muri hoi teenoor dié van Anemia wat solied of mikroporaat is.Supramurale skulptuur in Mohria en Anemia is perinies van aard Spore van die ander Schizaea-agtige varings toon geen of min verwantskappe met dié van Mohria en Anemia.By Actinostachys en Schizaea is die spore monolities en by Lygodium is hulle trileties maar die eksien is glad.The spore morphology of Anemia has been well documented (Mickel 1962;Hill 1977Hill , 1979;;Dettmann & Clifford 1991).Only recently, however, has their mor phology been appraised in a systematic context (De la Sota & Morbelli 1987; Dettmann & Clifford 1991).Since an intensive study of Mohria has been lacking for some time, the spore morphology of merely two or three species has been appraised in these studies.In a critical review of the genus, however, I found it to comprise seven species.The spore morphology of all the species recognised is investigated and their phylogenetic relationships evalua ted.

MATERIAL AND METHODS
For SEM study untreated sporangia and spores were af fixed to aluminium stubs using glue and sputter-coated with Au/Fd.Specimens were viewed in a Cambridge S200 SEM at 5 or 10 kV.Wax embedding was done using standard techniques.Sections 8 -10 p.m thick were serially sectioned with a rotary microtome and stained with safranin and fast green.Photography was done with a Zeiss 'Axoskop' fitted with a M35W camera.Ilford Pan F film was used for all photography.

Sporungial morphology
The sporangium morphology of the schizaealean ferns has been discussed by Goebel (1905).Prantl (1881) showed that sporangia of Mohria are derived from a single marginal protodermal cell, the position of which, as a result of continual adaxial growth, eventually becomes superficial.This has been confirmed by Bower (1918).Mohria, along with all the other schizaealean ferns, is generally considered as belonging to the leptosporangiates because of their single-layered capsule wall.Goebel (1905)  The number of rhomboidal apical plate cells varies.In M. saxatilis the cells may number three but in the other taxa there may be as many as six.Bierhorst (1971) considers a low number of apical plate cells as derived.Spore output per sporangium, even from the same frond, is extremely inconsistent.Bower (1923) gave the estimated number of spores per sporangium as 128 but reported counts of 101 and 107.The number, however, appears to be more variable, as I have made counts ranging from 57 to ± 196.Bower (1923) and Wagner (1974) associated a large spore output with the primitive state.In Anemia the sporangia are also short-stalked or sessile but with an ovate-globose to cylindrical capsule.Annuli are subapically positioned.

Schizaealean ferns are held together largely by the morphology of the sporangium with its group of radially arranged annulus cells which may be terminal or lateral.
Senftenbergia, a Carboniferous genus with a similar sporangium structure, has long been suggested as an ancient element of the schizaealean ferns (Radforth 1939).More recently, however, Mickel (1974) suggested that it is a member of the coenopteridalean ferns.If this is true, the 'schizaeoid' sporangium type must therefore have evolved more than once and thus cannot be used as a character diagnostic of the Schizaeales.The 'schizaeoid' ferns therefore appear to be polyphyletic.
defined leptosporangia as originating from a single cell and having a one-layered capsule wall.Eusporangia, on the other hand, develop from several cells and have, at least in the primordium, a many-layered capsule wall.In Mohria, neighbouring cells contribute to the formation of the massive stalk.Therefore, in gross morphology the sporangium of Mohria is intermediate between the two types.During the early development of the sporangium a tapetum cannot be distinguished.Later, however, it separates from the sporogenous tissue as a bicellular layer (Figure 1A & B).Cells of the outer tapetal layer are rectangular in transverse section and periclinal.The inner tapetal layer consists of much larger cells (Figure IB).Relatively early in the development of the sporangium the tapetum disintegrates leaving only the proximal part of the outer tapetal layer intact.In Mohria I found that the distal portion of the lamina curves around the sporangia in a protective manner.It does not differ morphologically or anatomically from the lamina tissue, and the sporangia are therefore exindusiate.Based on the grounds of outgroup comparison this feature is considered plesiomorphic.Anemia is also exindusiate.Sporangia in the schizaealean ferns are not borne in sori.In Mohria sporangia occur individually near each vein ending, or one or two sporangia may be borne at the terminal vein dichotomy.Sporangia in Mohria thus have a proper vascularization.In Anemia the vascularization is rudimentary or vestigial.Sporangia in Mohria are large, up to 670 /xm in diameter, globose and are borne on a short, massive stalk.The annuli, which are situated distally, consist of a single row of radially arranged elongated cells with densely lignified walls.These indurated cells may number up to 22.The stomium is formed by a few smaller cells with less ligni fied walls which interrupt the ring of annulus cells.The sporangia dehisce vertically with the slit always facing away from the lamina margin.