| Aspleniaceae | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Division: | Polypodiophyta |
| Class: | Polypodiopsida |
| Order: | Polypodiales |
| Suborder: | Aspleniineae |
| Family: | Aspleniaceae Newm. |
| Type genus | |
| Asplenium L. | |
| Genera | |
TheAspleniaceae (spleenworts) are a family offerns, included in the orderPolypodiales.[1] The composition and classification of the family have been subject to considerable changes. In particular, there is a narrowcircumscription, Aspleniaceaes.s. (adopted here), in which the family contains only two genera, and a very broad one, Aspleniaceaes.l., in which the family includes 10 other families kept separate in the narrow circumscription, with the Aspleniaceae s.s. being reduced to the subfamilyAsplenioideae. The family has a worldwide distribution, with many species in both temperate and tropical areas. Elongated unpairedsori are an important characteristic of most members of the family.
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Members of the family grow fromrhizomes, that are either creeping or somewhat erect, and are usually but not always unbranched, and have scales that usually have a lattice-like (clathrate) structure. In some species, for exampleAsplenium nidus, the rhizomes form a kind of basket which collects detritus. The leaves may be undivided or be divided, with up to four-foldpinnation. Thesori are characteristic of the family. They are elongated, and normally located on one side of a vein. More rarely, they may be in pairs on a single vein, but then they never curve over the vein. A flap-likeindusium arises along one edge of a sorus. The leaf stalks (petioles) have twovascular bundles, uniting to form an X-shape in cross-section towards the tip of the leaf. The stalks of thesporangia are one cell wide in the middle.[2]
The family Aspleniaceae was first described byEdward Newman in 1840.[3] Newman included three genera:Athyrium,Asplenium andScolopendrium.[4]Athyrium is now placed in a different family,Athyriaceae, not considered very strongly related to the Aspleniaceae, andScolopendrium is regarded as synonym ofAsplenium.[1]
The narrowcircumscription of the family adopted by thePteridophyte Phylogeny Group classification of 2016 (PPG I) recognizes only two genera,Asplenium andHymenasplenium.Asplenium has previously been split into a dozen or so genera, includingDiella, found only in Hawaii. The consensus ofmolecular phylogenetic studies is that all are nested withinAsplenium.[5][6] PPG I places Aspleniaceae in the suborderAspleniineae of the orderPolypodiales.
Earlier, Christenhusz and Chase had proposed a much broader circumscription of Aspleniaceae, in which it consisted of all the separate families that PPG I places in the suborder Aspleniineae (eight at the time), with the families reduced to subfamilies. Thus the Aspleniaceae of PPG I became the subfamily Asplenioideae.[7] As of July 2019[update], the broader circumscription of the Aspleniaceae is used byPlants of the World Online, which lists 24 genera.[8]
Aspleniaceae is placed in a clade known as eupolypods II, or more formally as suborderAspleniineae. The following cladogram, based on Lehtonen (2011)[9] and Rothfels & al. (2012),[2] shows a likelyphylogenic relationship between the Aspleniaceae and the other families in the clade.
| Aspleniineae (eupolypods II) | |
In the PPG I system, Aspleniaceae s.s. contains two genera:[1]
The Aspleniaceae have a worldwide distribution, with the large genusAsplenium being native to almost all parts of the world except Antarctica and some high Arctic areas.[10] The family is unusual in having high diversity in both temperate and tropical areas, and more-or-less equal numbers of terrestrial and epiphytic species. Plants are terrestrial, growing in the ground,lithophytic, growing on rocks, orepiphytic, growing on other plants; less often they are aquatic, growing in moving water.[2]
