Introduction To The Genus Fissidens And F. pallidinervis Central Floridian Mosses

Introduction To The Genus Fissidens And F. pallidinervis

Twenty species of the genus Fissidens  occur in Florida, according to Flora North America.  By definition all members of this genus have a peculiar flattened leafy shoot with double leaves.  At each node or insertion point along the stem there is a full-sized leaf and a smaller leaf. The leaves are attached sideways to the stem, creating a flat, frond- or feather-like shoot. The leaves do, however, tend to curl when dry. At the bottom of this post is my effort at a simplified, short-cut key to the species.

An image of Fissidens taxifolius illustrating the basic flattened shoot structure
 of the genus, with doubled leaf.  Image by Ralf Wagner.

As in most large moss genera, the individual species are distinguished by technical characters, mostly microscopic features of the foliage, and can only be definitively identified by experts.  However, there are some shortcuts that can help narrow down the choices in the relatively small number of species found in Florida (there are 450 species world-wide, 37 in North America), including the habit and length of the capsule stalks.

A dried specimen of Fissidens pallidinervis in the
herbarium at USF.  Note the relatively short stalks
of the capsules (sporangia), and the twisted  dry
leaves.

Fissidens pallidinervis Mitten is relatively common in Florida, from the panhandle to the keys.  It is documented elsewhere only in Louisiana, but might be expected to show up in southern Georgia, Alabama, and Mississippi.  It typically occurs in moist areas at the bases of trees or on decaying logs, but found in our area also on shell mounds.

 From the other 19 species it is distinguished by a combination of  details, mostly of the leaves.  The cells of the leaf, on either side of the prominent midrib, are tiny, roundish and papillate, which means they bear small, translucent bumps on their surface.  This species has 2 or more such bumps, while some species have only one, and others have none (are completely smooth).

A single shoot from the specimen above.  Note that three
sporangia are rising from a single point on the stem.

The leaf cells of  Fissidens are small and roundish.  In this view,
the papillae can be detected as tiny bright spots of lighter
green.

The shoots are tiny, about _mm long, and each may produce 2 or more sporangia near the shoot tip.  The stalks of the sporangia are relatively short, compared to other members of the genus, about 2 mm long. Only F. leptophyllus is in the same range, but in that species there is a clear limbidium ( a row of scleried-like cells) on the lower margin of the leaf, the leaf cells bear only 1 papilla, or are only rounded.  While others are variable, with stalks sometimes in this range, they are usually longer.
















Provisional short-cut key to the species of Fissidens in Florida.

1_Aquatic
2_Sporangium stalks .5-.6mm����.F. fontanus
2_Sporangium stalks .7-1.5 mm���.F. hallianus
1_Terrestrial
3_Sporangium stalks less than 6 mm long
        4_Occurring on bark, tree bases, not soil-specific
                   5_Sporangium stalks to 2 mm long
                         6_Leaf cells rounded or with one papilla; bases of trees, cypress swamps
                                                       �������..............��..F. leptophyllus 
                         6_Leaf cells with several small papillae; bases of trees.....�F. pallidinervis 
                   5_Sporangium stalks 3.5-5 mm long
                        7_Leaf cells smooth to 1 papillate
                              8_Leaves up to 6 pairs, markedly toothed, cells 1-papillate; on bark,                                                                     logs, cypress trees�....F. serratus 
                           8_Leaves up to 25 pairs, not toothed, cells smooth to rounded; Bark, tree                                                             bases, rotten wood .................�.F. santa-clarenis 
                              8_Leaves up to 10 pairs, minutely toothed, leaf cells smooth to bulging;                                                               bases of trees, soil............................�....... F. amoenus 
                      7_Leaf cells with several small papillae; leaf apex ending in a sharp, clear                                                               cell, on soil, banks, roadsides,  uprooted trees ��.F. elegans
           4_Occurring on calcareous soil or rocks
                    9_ Found throughout Florida 
                            10_ occurring primarily at bases of trees; leaves in a pinnate pattern, up to 28 pairs
                                    ..........................................F. subbasilaris              
                            10_ on moist limestone in ravines; Leaves in a palmate pattern, up to 12 pairs .
                                    ......................................................F. zollingeri 
                    9_Found in north Florida only; on wet soil or rocks along streams, 
                            11_ Found in Florida panhandle *;soil, rocks and stones in shaded  ravines                                                               ���......................................................��..���..F. pellucidus 
                           11_Found in northern peninsular Florida, stems branched,........F. obtusifolius
                          11_Found in northern peninsular Florida*, stems unbranched �F. minutulus 
3_Sporangium stalks to 10-11 mm long
                            12_Capsules somewhat asymmetric, 1 mm long; occurring on bare, often clay, soil 
                                  .......................................................................................�.. F. bushii 
                            12_Capsule 1.8 mm long; occurring at bases of trees, roots�......... F. dubius 
                            12_ Capsules symmetric; bases of trees, soil, logs .................��.F. bryoides 
3_Sporangium stalks to 15 mm long
                          13_ Capsules to 2.5 mm long, symmetric; on calcareous soil, north Florida only
                                                  ................................������..F. polypodioides 
                          13_ Capsules to 1.5 mm long, asymmetric; seeps, moist rocks, soil;  central Florida
       3_Sporangium stalks to 25 mm; on seeps and rocks with dripping water���.. F. adianthoides 
       3_Sporangium stalks to 17 mm; on moist soil .humus, .rocks ................................��.. F. taxifolius 

*Questionable records of F. pellucidus and F. minutulus in Collier County, far removed from their north Florida ranges