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tasmanian liverworts - metzgeriaceae

metzgeria 101025B

Metzgeria 101025B
1. ventral surface with pair of globular male branches along the mid-rib

 

Discovered growing as an epiphyte on Cassinia aculeata in wet scerophyll forest. Plants are minute; mature thalli with midribs measured at 0.65 mm. Detached gemmae are much narrower but we have no idea at what stage these may be termed thalli - detached, development of costa, development of next generation of gemmae? Separating the weft yielded large numbers of gemmae of many sizes in various stages of development.

The most significant feature of this specimen is that it lacks bifurcation of thalli and permanent branching we had observed on other species. While marginal branching is profuse these are all attached by few cells (pix 1, 2, 5 & 11) suggesting gemniferous origin. What may be unusual for a Metzgeria is the apparent development of gemma at the distal end of thallus (pix 5). Thalli have none to few single hairs on the ventral side of younger plants but older bodies sport more on both margins and mid-rib but none on the dorsal side. A few hairs measured average 57 x 10.5 µm. Regular ventral branching was not observed.

Mid-rib consists of 2 elongated cells width on the slightly convex dorsal as well as ventral sides. Some freshly seperated thalli lacked mid-ribs (pix 9); these (or at least the cortical cells) start developing as can be seen in pix 4. Other thalli have discontinuous midribs with nerve cells missing (pix 6). Pix 11 shows that gemmae production is possible in the absence of central nerve. Laminal cells (pix 7) are isodiametric, 30-40 µm across with relatively thick walls; numerous small dark oil bodies, numbers undetermined; trigones absent; mid-rib cells are elongated. There are 3-5(-9) laminal cells between mid-rib and margin.

Many thalli, including some freshly separated gemmae, had globular male branches (pix 3). Several months later (mid-March) we observed antherida on some thalli but no perianths. In the case of a population of M. decipiens tracked there was a lag of 5 months between observing mature antheridia and sporophytes dehising. On the other hand this this is consistent with So's observation1 that many species are 'known only in the sterile condition or only from male or female plants'.

So's paper2 on M. submarginata may throw some light on the subject by suggesting that 'prolific production of gemmae and secondary gemmae seems to show that the population is permanently reduced to the juvenile stage'. This may be the case here but the presence of antheridia suggests our specimen is capable of sexual reproduction even if fruiting has not been sighted.

So's key1 for Australasia provides no match for this specimen. Lack of bifurcation for a Metzgeria is so distinctive that it could not possibly be overlooked in the literature.

We have made no attempt to survey the population but several C. aculeata nearby appeared to be hosting the same liverwort. Subsequently we discovered another population on the same host several km away.

A specimen has been lodged with HO.

(Note: pix #8 of antheridia was taken 5 months after #3 of male branch.)


2. marginal gemmae

3. male branch

4. midrib cells forming

5. terminal gemma

6. discontinuous midrib

7. lamina cells

8. antherida

9. midrib absent

10. gemma initiation?

11. gemmae

Literature
- Meagher, D, & Fuhrer, B., A Field Guide to the Mosses and Allied Plants of Southern Australia, (ISBN 0 642 56828 6), Flora of Australia Supplementary Series, Number 20 - Australian Biological Resources Study/The Field Naturalists Club of Victoria, 2003
- Meagher, D. 'Studies on Victorian Bryophytes 6. Key to thallose liverworts and hornworts', in Victorian Naturalist Vol. 123(4) August 2006 pp 247-254 (specifically disclaims application outside the state of Victoria)
- Key to Australasian Liverwort and Hornwort Genera (ISBN 0 642 56840 5) on CDRom ('Lucid Key')

Web
- 1So, M.L., 'Metzgeria (Hepaticae) in Australasia and the Pacific', New Zealand Journal of Botany, 2002, Vol.40: 603-627 provides a key to a wider range of species but it has not proven useful in this context
- 2So, M.L., 'Metzgeria submarginata sp. nov., a 'new' species from Australia and New Zealand' New Zealand Journal of Botany, 2002, Vol. 40: 201-205
- da Costa, D.P., 'Morphology of Metzgeria conjugata Lindb. (Metzgeriales, Hepaticopsida)' Tropical Bryology 6: 65-69, 1992 has some SEMs of reproductive structures used to identify the male branches

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