Davallia J.E. Smith
- Protologue: Mém. Acad. Sci. Turin 5: 414 (1793).
- Family: Davalliaceae
- Chromosome number: x= 40;D. denticulata, D. solida: 2n= 80
Major species and synonyms
- Davallia denticulata (Burm.f.) Mett. ex Kuhn, Filic. decken.: 27 (1867), synonyms: Adiantum denticulatum Burm.f. (1768), D. elegans Swartz (1801), Trichomanes chaerophylloides Poir. (1808).
- Davallia falcinella C. Presl, Reliq. haenk. 1: 66, t.11, f. 2 (1825), synonyms: Leocostegia falcinella (C. Presl) J. Smith (1842), Humata falcinella (C. Presl) Copel. (1905), Trogostolon falcinellus (C. Presl) Copel. (1927).
- Davallia parvula Wall. ex Hook. & Grev., Icon. filic. t. 138 (1829), synonyms: Humata parvula (Wall. ex Hook. & Grev.) Mett. (1856), Leucostegia parvula (Wall. ex Hook. & Grev.) Bedd. (1883).
- Davallia solida (G. Forst.) Swartz, Journ. Bot. (Schrader) 1800: 87 (1801), synonyms: D. pyxidata Cav. (1802), D. fejeensis Hook. (1845), D. robinsonii Copel. (1926).
- Davallia trichomanoides Blume, Enum. pl. Javae: 238 (1828), synonyms: D. bullata Wall. ex Hook. (1845), D. lorrainii Hance (1866), D. barbata Alderw. (1911).
- General: foot ferns, ball ferns, basket ferns (En).
- D. denticulata : Toothed davallia (Am)
- Indonesia: paku tertutup (Malay), pulak, pullaka (Alor)
- Malaysia: paku tertutup
- Thailand: naakkharaat (central, peninsular)
- Vietnam: răng dà hoa có răng.
- D. parvula: Malaysia: paku lumut batu.
- D. solida : Polynesian foot fern, rabbit's foot fern (En)
- Indonesia: paku kalici
- Thailand: phaya nakkharat (northern), wan nakkharat (central), neraphusi (north-eastern).
- D. trichomanoides : Japanese ball fern, squirrel's foot fern (En).
Origin and geographic distribution
Davallia is widely distributed in the Old World tropics, with its greatest diversity in Malesia where 23 species (9 endemics) occur. Only D. canariensis (L.) J. Smith is native to South-West Europe. D. denticulata is distributed from tropical and southern Africa, Madagascar, Indian Ocean islands (Comores, Seychelles, Christmas Islands), Sri Lanka, India, Thailand, Burma (Myanmar), China (Hainan), Indo-China, throughout Malesia, Australia (Queensland) to the islands in the Pacific. D. falcinella occurs in the Philippines and the Marquesas Islands. D. parvula occurs in Papua New Guinea, Borneo, East Sumatra and Singapore. D. solida is distributed from India, throughout South-East Asia to Australia and the Pacific. D. trichomanoides is widely distributed from India, China and Japan throughout South-East Asia.
Most Davallia species are epiphytes and several are grown for their creeping surface rhizomes, densely covered with red-brown scales and sometimes hairs, overall resembling various animal feet. They are often attractive indoor ornamental plants, grown in pots or in hanging baskets. The leaves are used fresh or dried in floral arrangements. The term ball ferns originates from Japan, where the flexible rhizomes of D. trichomanoides are tied into balls and other figures; when these figures are hung and watered, new leaves will subsequently appear on the surfaces, and they become self-contained hanging baskets. The leaf and rhizome of D. solida are popular ingredients in mixed medicines of Polynesian local healers.
Production and international trade
Several Davallia species, particularly those mentioned here, are popular ornamentals worldwide, but no local or international statistics on trade or production are available. Fresh and dried leaves are offered for sale at local florists for use in floral arrangements.
The presence of vicianin, a cyanogenic glycoside, has been found in several Davallia species (e.g. D. denticulata, D. trichomanoides ). Usually, cyanogenesis (production of the dangerous hydrocyanic acid) only occurs after maceration of the plant tissue. In D. trichomanoides available cyanogenic disaccharides are degraded by the also available β-glycosidase into hydroxynitriles and the corresponding disaccharides. The hydroxynitriles may decompose either spontaneously or enzymically (hydroxynitrile lyase) to produce hydrogen cyanide and an aldehyde or ketone. From the rhizomes of D. mariesii T. Moore ex Baker (distributed in Taiwan, Korea, Japan), the following compounds were isolated: davallin (a tetrameric proanthocyanidin), procyanidin B-5, epicatechin-(4 β-8)-epicatechin-(4 β-6)-epicatechin, and epicatechin-(4 β-6)-epicatechin-(4 β-8)-epicatechin-(4 β-6)-epicatechin, which showed an inhibitory effect toward protein kinase C; also a γ-lactone derivative named davallialactone and the 7-O-β-D-glucuronide of (+/-)-eriodictyol along with caffeic acid, 4-β-D-glucopyranosylcaffeic acid and 4-O-β-D-glucopyranosyl-p-coumaric acid.
Small to rather large epiphytic or epilithic ferns with creeping rhizomes, roots restricted to the ventral side of lateral buds. Rhizomes fleshy, usually long and somewhat flattened, densely covered with scales; scales peltate or basifixed with cordate base and overlapping lobes, variously shaped. Leaves alternate, arranged in 2 rows; petiole usually well-developed, articulated to the rhizome, sulcate adaxially; lamina triangular-oblong, pentagonal or lanceolate in outline, usually firm in texture, simple, trifoliate or 2-5-pinnately compound with the pinnae further pinnatifid, usually with glandular hairs when young; veins distinct; "false veins" (bands of regularly arranged short cells without stomata) sometimes present between the veins. Fertile leaves often with leaflets or segments narrower than the sterile ones; sori commonly borne separately on small oblique lobes, terminal on the veins, close to the margin; indusia attached by their base and sides, only the upper edge free, forming a cup-shaped structure. Spores bilateral, monolete, ellipsoid, 25-60 μm long, light brown and translucent, densely subverrucate-areolate.
- D. denticulata . Rhizome without scales 3-15 mm in diameter; scales peltate, 4-8 mm × 0.5-1.5 mm, narrowing evenly towards the apex or narrowing abruptly from a broad base, toothed, red-brown to black. Petiole 4-50 cm long, green or more or less dark brown, with two pale green longitudinal lines near the adaxial surface, glabrous or with few deciduous scales at the base; lamina broadly triangular in outline, (16-)30-60(-90) cm × 13-50 cm, bipinnate to quadripinnate, leathery, shiny; petiolules 4-35 mm long; pinnae broadly deltoid, largest ones 8-45 cm × 5-30 cm, often tapering into a long point; largest pinnules triangular, 0.7-20 cm × 0.4-11 cm; ultimate segments linear or narrowly ovate, 5-27 mm × 2-6 mm, with very oblique, rounded, shallow or deep lobes, the fertile lobes with somewhat narrower segments than those of the sterile ones; veins free, mostly forked, raised on the lower surface, with false veins between the outer branches, reaching almost to the vein junctions. Sori separate, several borne on a segment at the forking point of veins; indusium pouch-shaped, truncate to slightly rounded, 1-1.3 mm × 0.5-1 mm, extending to lamina margin or not; lamina usually extending into a small, incurved tooth at one or both sides of a sorus. Spores shallowly verrucate with a short aperture.
- D. falcinella . Rhizome without scales up to 3 mm in diameter; scales peltate, acicular, 6-10 mm × 2 mm, nearly black, at distal part with marginal setae. Petiole 4-9 cm long, dark brown; lamina deltoid, 7-14 cm × 6-14 cm, 3-4-pinnate; petiolules 1-7 mm long, pinnae linear-triangular, 4-7 cm × 2-7 cm; pinnules linear-oblong, 15-25 mm × 7-12 mm; ultimate segments without a tooth, 1-2 mm long and wide (in sterile leaves up to 4 mm long); veins in sterile ultimate lobes frequently simple, not reaching the margin, false veins absent. Sori separate, often single on a segment, at the forking point of veins; indusium attached at base and only part of the sides, semicircular, about 1 mm in diameter; lamina not extending into teeth beyond a sorus. Spores irregularly verrucate.
- D. parvula . Rhizome without scales 0.5-1.2 mm in diameter, white waxy; scales peltate, narrowed evenly towards the apex, 2.5-6 mm × 0.3-0.6 mm, red-brown, in distal part with marginal setae. Petiole (0.1-)1-5 cm long; lamina deltoid, 0.6-4 cm × 0.5-3.5 cm, entirely divided into fine linear segments without obvious rachis; longest petiolules 1-2 mm long; ultimate segments 0.5-4 mm × 0.2-0.4 mm, obtuse or acute without a tooth with simple veins reaching the margin, false veins absent. Sori separate, often single on a segment at the forking point of veins; indusium only attached at the base, semicircular to subtriangular, 0.3-0.8 mm in diameter, upper margin not elongated; lamina usually extending beyond it at either side for 1-1.5 mm into two unequal arms.
- D. solida . Rhizome without scales 4-14 mm in diameter; scales peltate, narrowing evenly towards the apex, 5-10 mm × 1-1.2 mm, red-brown to black, when young bearing woolly, multiseptate hairs but when old covered with appressed bases of scales only, the distal parts of scales being deciduous. Leaves dimorphic; petiole 9-35 cm long, distinctly grooved adaxially; lamina broadly deltoid, 15-90 cm × 21-40 cm, 2-3-pinnately compound; petiolules 5-25 mm long; longest pinnae deltoid, 11-28 cm × 6-15 cm; longest pinnules triangular, 4-10 cm × 1.5-8 cm; ultimate segments 10-40 mm × 3-17 mm, usually lobed, with pinnate veins, false veins absent. Sori separate, several borne on a segment at the forking point of veins; indusium also attached along the sides, 1.2-2 mm × 0.5-1 mm, upper margin not elongated; lamina not extending into teeth beyond a sorus. Spores prominently verrucate.
- D. trichomanoides . Rhizome without the scales 3-8 mm in diameter; scales peltate, nearly acicular above a broad base, 4-8 mm × 1-1.5 mm, brown to red-brown, toothed or with marginal setae in distal part. Petiole 4-20 cm long; lamina deltoid, 10-35 cm × 9-25 cm; petiolules 1-6 mm long; pinnae 5-19 cm × 3-12 cm, pinnules 2-7 cm × 1-3 cm, ultimate segments 5-27 mm × 2-6 mm; veins in ultimate lobes simple or forked but not reaching the margin; false veins are usually present; indusium also attached along the sides, 1.2-2 mm × 0.5-1 mm, upper margin not elongated; lamina usually extending into a tooth at either side of a sorus, teeth equal in size. Spores verrucate, aperture nearly equal to their length.
Growth and development
The leaves of Davallia are articulated to the rhizome and are deciduous when old. They do not usually fall off at a definite season, but in D. denticulata and D. solida all leaves on a plant drop together, and this is followed rapidly by the growth of new leaves. In strongly seasonal climates the leaves fall as soon as the dry season is well established, and the plants rest in a leafless condition until the next rainy season. In non-seasonal climates plants are never bare of leaves for long. The deciduous habit is of great value for adaptation to seasonal climatic conditions. Environmental conditions such as relative humidity, light intensity, soil moisture content, soil nutrients affect the population density of the fern and the size of leaves. In the rainy season the number of leaves increases. Ferns growing under shade produce bigger leaves but fewer in number compared with those exposed to sunlight. Fertile leaves may occur the whole year round.
Other botanical information
Davallia comprises 35-90 species, depending on the delimitation of the genus and its species. The smaller species with the indusium not attached to the sides, but only to the base, have often been separated into the genus Humata Cav.
The false veins in D. denticulata indicate that the present leaflets originated during evolution by joining of initially highly dissected segments. The false veins correspond to the lines along which the initial segments were joined. The inner tissue below the false veins has no air-spaces which makes it more translucent. Most other Davallia species have lost such characteristics.
Sometimes 2 varieties are distinguished in D. denticulata : var. denticulata and var. elata (G. Forst.) Kuhn. In var. denticulata , the indusium is attached at the base but also along the sides and the upper margin not elongated; in var. elata , the indusium is attached at the base and only at some parts of the sides, and the upper margin is elongated.
D. parvula is closely related to D. repens (L.f.) Kuhn, with which it possibly also hybridises. D. repens is a very variable species, distributed almost as widely as the genus, possibly hybridising with several related species; it occurs in purer form at lower altitudes and in areas where no related species are found. In general the lamina of D. parvula is more completely divided and into finer linear segments, without a clear rachis, than the lamina of D. repens .
D. solida is a very variable species which in a broad species concept is subdivided into 3 varieties: var. solida (distribution similar to the genus in Asia), var. pyxidata (Cav.) Noot. (occurring only in Australia: Queensland and New South Wales) and var. fejeensis (Hook.) Noot. (occurring in Fiji and the Austral Islands). In a narrow concept the varieties are considered as separate species. The major differences between the varieties are the size and the rate of division of the lamina: the ultimate segments of var. solida are 10-40 mm × 3-17 mm, of var. pyxidata 5-20 mm × 3-8 mm, of var. fejeensis 3-5 mm × 0.2-1 mm. Var. fejeensis in particular has many cultivars (e.g. "Dwarf Ripple", "False Plumosa", "Plumosa").
In D. trichomanoides plants with nearly black scales on the rhizome and with highly contrasting white setae have been classified as var. lorrainii (Hance) Holttum.
Davallia species are perfectly adapted to epiphytic conditions and most of them can stand more exposure than most other epiphytes, which explains the wide distribution of the genus. Several species can withstand short periods of mild frost (e.g. D. canariensis (L.) J. Smith, D. trichomanoides ), but in general optimum temperatures for growth lie between 30-35°C. Although commonly found growing on the ground in Australia, D. denticulata is an epiphytic fern found on trunks of many different tree species and often growing together with other ferns such as Asplenium nidus L. or Platycerium bifurcatum (Cav.) C. Chr. It also can be epilithic on granite, limestone or sandstone, or terrestrial on different soils, in forests and in exposed locations, from sea-level to 2200 m altitude. D. denticulata is one of the commonest epiphytic ferns in South-East Asia, particularly on trees near the sea. D. falcinella is epiphytic, D. parvula epiphytic or epilithic, both species growing from sea-level up to 800 m altitude. D. solida is epiphytic or epilithic. It grows on different kinds of rock, or terrestrial on different soils, as well as in exposed locations as in deep shade, from open rocky places and savannas to primary rain forest, up to 1500 m altitude. D. trichomanoides occurs epiphytically on mossy branches and tree bases and epilithically on different kinds of rock, mostly in wet locations, but sometimes in dry exposed conditions, at altitudes of 100-3500 m.
Propagation and planting
Although spores germinate easily, Davallia is usually propagated by rhizome parts. In the wild the rhizomes grow uncovered, so care must be taken when planting not to bury them (especially the growing tips) completely in the planting medium. Uncut sphagnum or a very loose well-drained potting mix is a suitable medium for planting. Propagation by tissue culture using growing points of the rhizomes has also been successful.
Most Davallia species are easy to cultivate. Since they are epiphytes they require good drainage whereas their roots need adequate moisture. If conditions are too wet rhizomes turn dark and soft. Rhizomes that shrink or shrivel due to lack of water are very slow to recover. Deciduous species should be kept moist during dormancy but not overwatered. Bright indirect light produces finer growth than medium or low indirect light. Regular application of fertiliser during the growing period is beneficial. To keep plants more compact and to encourage lateral branches to sprout, rhizome tips that are over 5 cm long can be cut off.
Genetic resources and breeding
Neither germplasm collections nor breeding programmes are known to exist for Davallia .
Since several Davallia species are attractive and decorative indoor or outdoor ornamental ferns, further research on domestication and the most suitable cultivation requirements are worth considering.
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Titien Ngatinem Praptosuwiryo & P.C.M. Jansen