Asplenium tutwilerae

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Asplenium tutwilerae
Asplenium tutwilerae incorporated into a green wall at Longwood Gardens

Critically Imperiled  (NatureServe)
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Division: Polypodiophyta
Class: Polypodiopsida
Order: Polypodiales
Suborder: Aspleniineae
Family: Aspleniaceae
Genus: Asplenium
Species:
A. tutwilerae
Binomial name
Asplenium tutwilerae
B.R.Keener & L.J.Davenport

Asplenium tutwilerae (Tutwiler's spleenwort or Scott's fertile spleenwort) is a rare

diploid A. × ebenoides, a hybrid of A. platyneuron and A. rhizophyllum. Except for its spores, which are fertile rather than malformed, A. tutwilerae is essentially identical to A. × ebenoides and was described as part of that species until 2007. It is named in honor of Julia Tutwiler
, who discovered the only known wild population at Havana Glen in 1873.

Description

Asplenium tutwilerae is a small, compact, evergreen, rock-inhabiting fern that grows in individual clumps. It displays a slight frond dimorphism, with the larger, fertile leaf blades more or less upright, while the smaller, usually sterile blades are tightly pressed against the ground.[1]

Many threadlike roots, up to 6 centimeters (2 in) long, are attached to the rhizome, which may be horizontal or upright. The rhizome may be 0.5 to 2 centimeters (0.2 to 0.8 in) long and 0.3 to 0.5 centimeters (0.12 to 0.20 in) in diameter. Both roots and stipes (the stalk of the leaf, below the blade) may sprout along the length of the rhizome, which is covered in scales near its upper tip. The scales are narrowly triangular in shape, and range from 1 to 4 millimeters (0.04 to 0.2 in) long and 0.2 to 0.5 millimeters wide. The scales are translucent, but are covered with a dark clathrate (lattice-like) network,[1] giving them a stained-glass-like appearance.[2]

The stipe is shiny and chestnut-brown to purplish brown in color. The lowest quarter of the stipe is scaly, while the upper half is hairy. The scales resemble those of the rhizome, diminishing in size and particularly in width, taking on a linear shape. The hairs are orange-reddish in color, and become thicker towards the tip. In smaller fronds, the stipe is 0.5 to 2.5 centimeters (0.20 to 0.98 in) long, while in the larger fronds, it is 2.0 to 9 centimeters (0.8 to 4 in) long.[1]

The shape of leaf blades in A. tutwilerae is quite variable. The leaves are green in color, not leathery (unlike some other Asplenium species), and both leaves and their

tetraploid, with a sporophyte chromosome number of 2n = 144.[1]

The smaller, ground-hugging fronds are lance-shaped, ranging from 2 to 11 centimeters (0.8 to 4.3 in) long and 1 to 2 centimeters (0.4 to 0.8 in) across. The basal half to two-thirds of the blade is cut into lobes; they are occasionally cut all the way to the rachis to form pinnae at the very base. The apical part of the frond slowly tapers to a tip; its edges range from lobed to very slightly serrated. They do not generally have more than one pair of pinnae, if they have them at all. When the pinnae exist, they are roughly oval-shaped, with the ovals widest towards the base, 0.5 to 0.9 centimeters (0.2 to 0.4 in) long to 0.4 to 0.5 centimeters (0.2 to 0.2 in) across, with squared-off bases, blunt tips, and no teeth. The lobes are similar in shape to the pinnae, 0.3 to 1 centimeter (0.1 to 0.4 in) long and 0.2 to 0.4 centimeters (0.08 to 0.16 in) wide, with blunt tips; their edges may be entire (toothless) or have small, wavy serrations. These fronds are, occasionally, fertile, in which case they bear from 1 to 3 sori per pina or lobe in the more basal part of the frond; in the more apical part of the frond, each lobe or tooth on one side of the midrib bears a sorus.[1]

The larger, more upright fronds are also lance-shaped, measuring from 7 to 18 centimeters (3 to 7 in) long and 2 to 8 centimeters (0.8 to 3.1 in) across. They are more deeply cut than the smaller fronds; the basal one-quarter to one-third of the blade is cut into pinnae, the middle half is lobed, while the remainder tapers towards the tip much like the smaller fronds, with irregular margins. Specimens occasionally form buds at the leaf tip which can develop into new plants. The larger fronds typically have one to two pairs of lance-shaped pinnae, 0.7 to 2 centimeters (0.3 to 0.8 in) long and 0.4 to 1 centimeter (0.2 to 0.4 in) in width. The pinnae are squared off at the base, sometimes bearing "ears". They may be blunt- or pointed-tipped, and their edges may be entire or have small, wavy serrations. The lobes of the larger fronts are similar in form to the pinnae; they may be smaller or larger than the pinnae (giving the frond an asymmetrical appearance), ranging from 0.3 to 5 centimeters (0.1 to 2 in) in length and 0.3 to 1 centimeter (0.1 to 0.4 in) in width.[1]

A. tutwilerae is most likely to be confused with A. × ebenoides, from which it can be distinguished by its fertile, well-formed spores (as opposed to the malformed, sterile spores of the latter).

backcrosses with A. platyneuron to form the sterile triploid A. × boydstoniae, but the hybrid's morphology is much closer to A. platyneuron. Its blade is fully cut into pinnae, and the principal resemblance to A. tutwilerae is in the long apex of the blade, lacking in A. platyneuron.[3] A triploid backcross hybrid between A. rhizophyllum and A. tutwilerae was accidentally produced in culture. It resembled walking fern and had proliferating tips, but the basal portion of the leaf was sporadically and irregularly cut into sharp-pointed lobes (never pinnae) in a manner resembling Scott's spleenwort, and the edge of the long, drawn-out apical portion of the leaf had shallow undulations rather than being a smooth curve. The stipe was maroon, the color extending only a short distance into the rachis.[4]
Apart from the geographical confinement of A. tutwilerae, it can generally be distinguished from other spleenworts by the same characters as A. × ebenoides.

Taxonomy

The species was originally discovered in

allopolyploidy and were tetraploid.[8]

Wagner went on to sow a large number of spores from a Maryland population of A. × ebenoides on culture media. While the vast majority of these were sterile, a small number were unreduced, diploid, and fertile.[a] When these diploid spores fertilized one another, they formed allotetraploid zygotes that grew into sporophytes. The resulting sporophytes showed a number of differences when compared with the Alabama plants: they were lighter green, more delicate in texture, had wider and more regular blades, and had slightly but distinctly toothed edges. Other than these differences, they very closely resembled the diploid Maryland population from which they originated. Wagner argued that these changes reflected differences in genotype between the original A. platyneuron and A. rhizophyllum individuals that had given rise to the two populations.[9]

Wagner preferred to treat both sterile and fertile A. × ebenoides as

species concepts, and warranted recognition as a species. The segregation of A. tutwilerae from A. × ebenoides made it one of the rarest fern species worldwide.[1]

Distribution

Asplenium tutwilerae is only found in Havana Glen and some of the small neighboring ravines. As of 1982, 200 to 300 individuals were believed to grow in Havana Glen proper.[11]

Ecology and conservation

Asplenium tutwilerae is found growing on ledges of

siliceous pebbles in a matrix rich in iron, with a little calcium. The thin soil formed from the decomposed rock is minimacid.[12] The ferns grow largely on the rocks, which are coated with mosses and lichens, rather than the forest floor.[11]

While A. tutwilerae can, like A. rhizophyllum, form proliferating buds at the leaf tip, these are quite rare and play no significant role in its reproduction. Propagation is almost entirely through spores.[11]

The Alabama Plant Conservation Alliance is working to monitor and conserve the single wild population of A. tutwilerae.[13]

Cultivation

The plant is sometimes cultivated as a greenhouse or garden ornamental. It can be grown in moist potting mix,

cow manure, crumbled plaster (to provide calcium), crushed charcoal, and gravel. They were kept at all times above 70 °F (21 °C) and watered sparingly with rain water.[15]

Notes and references

Notes

  1. haploid spores with a chromosome number one-half that of the sporophyte. Because A. × ebenoides contains chromosomes from two different parental species, its homologous chromosomes cannot successfully pair to initiate meiosis. In an unreduced spore, the spore has formed directly from the sporophyte by meiosis
    and has the same chromosome number as the sporophyte.

References

  1. ^ a b c d e f g h Keener & Davenport 2007.
  2. ^ Cobb, Farnsworth & Lowe 2005, p. 59.
  3. ^ Wagner 1956.
  4. ^ Wagner & Boydston 1958.
  5. ^ Davenport 2012.
  6. ^ Leggett 1873.
  7. ^ Underwood 1896.
  8. ^ Wagner 1953.
  9. ^ Wagner & Whitmire 1957.
  10. ^ Wagner, Moran & Werth 1993.
  11. ^ a b c Walter, Wagner & Wagner 1982.
  12. ^ Wherry & Trudell 1930.
  13. ^ APCA 2012.
  14. ^ a b Hoshizaki & Moran 2001, p. 198.
  15. ^ Irving 1949.

Works cited

External links

Data related to Asplenium tutwilerae at Wikispecies

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