Native Plants of Hawai‘i - Sadleria cyatheoides

Sadleria cyatheoides

Blechnaceae or Chain fern family

Synonyms: Blechnum cyatheoides, Blechnum fontanesianum, Blechnum kaulfussianum, Woodwardia cyatheoides

ʻAmaʻu

ʻAmaʻumaʻu, ‘Āmaʻumaʻu, Maʻu, Maʻumaʻu, Puaʻa ʻehuʻehu

Rasp fern, Red pig

Natural Range & Environment

Sadleria cyatheoides is endemic to all the main Hawaiian Islands except Ni‘ihau and Kaho‘olawe. It is a common fern found in exposed habitats, mesic to wet forests and shrublands, and a pioneer species on new lava flows, from (5–)75 to 2,200 m ((16–)246 to 7,218 ft) [Palmer 2003].

ʻAmaʻu has long linear sori on the pale underside of its fronds (Photograph courtesy of Forest & Kim Starr CC BY 3.0 US.). ʻAmaʻu fiddleheads, as well as the base of older fronds, are covered with hair-like scales (pulu). Young ʻamaʻu fronds are bright red (Photograph courtesy of Forest & Kim Starr CC BY 3.0 US.). Two clusters of wild ʻamaʻu: younger plants clinging to a cliff face (Photograph courtesy of Forest & Kim Starr CC BY 3.0 US.); and much taller and older plants (Photograph courtesy of Blaine T. Spellman CC BY-NC 4.0.). Two cultivated ʻamaʻu: one upright (Photograph courtesy of mtntopview CC BY-NC 4.0.); and one that has fallen over (Photograph courtesy of Daderot public domain), something that seems to happen often in cultivation. Header photograph courtesy of Forest & Kim Starr CC BY 3.0 US.

Description

Sadleria cyatheoides is a medium-sized to large (up to 13 ft [4 m]) [Palmer 2003] upright or decumbent fern with a lifespan well in excess of five years. Erect cultivated (and wild?) ʻamaʻu frequently fall over to become decumbent. Its trunk is not made of bark and wood, but rather is a thick fibrous rhizome with a starchy pith.

Sadleria cyatheoides has erect (i.e., non-drooping) fronds (blade and stipe combined) anywhere from about two to ten feet (0.6 to 3 m), primarily dependent on the age of the plant. Young fronds are a bright red, turning green when mature. Frond stipes are straw-colored, grooved, and naked (i.e., without scales) except at their base. Fiddleheads and young blades are covered with tan to brown pulu (scales) but become naked as they mature. The leathery blades are 1-pinnate to 2-pinnate (at their base) with a glossy dark green upper surface and a pale to whitish lower surface when mature. Veins are nearly invisible except near the pinnae margins. Old dead fronds are retained and form a "skirt" around the base of the fern.

Sadleria cyatheoides, like the other Sadleria species, has long linear sori positioned in the center of the pinnules. The indusia (outgrowths of the blade that covers the sori) open inward. Species of Sadleria are divided and identified by frond size and droopiness, visibility of veins, and the shape, color, and abundance of scales.

Growth Requirements

General

Based primarily on my (Koebele) failures, the secret to successfully growing ʻamaʻu is keeping the temperature down and the humidity up. Growing ʻamaʻu in places like Volcano (on Hawai‘i Island) or the back of Mānoa Valley (on O‘hau) — the sites of the two photographs above — is much easier than trying to grow this beautiful fern in Pearl City, O‘ahu. However, if you DO live in a hot and dry place like Pearl City, there are things you can do to improve growing conditions.

First, while at higher, cooler elevations, both wild and cultivated ʻamaʻumaʻu can survive being out in the open and exposed to the full sun, down below 500 ft, it's unwise to plant your ʻamaʻu in a site that receives any direct sunlight at all. Rather, find a bright but shaded spot for your ʻamaʻu to grow.

Similarly, rainy and humid places can compensate for high temperatures, so if your place is both hot and dry, set up a sprinkler or misting system in your landscape to keep the evaporation from the fronds of your ʻamaʻu at a minimum. Set the system to turn on multiple times each day (it doesn't have to be for long, just a minute or two), particularly around midday and early afternoon. The brief shower or misting will both wet the fronds of your ʻamaʻu and evaporatively cool the entire site.

Like nearly all ferns, ʻamaʻu needs moist to wet soil or media that also drains water quickly. Lava/cinder or organic-dominant soils are best, but I've also grown ʻamaʻu in clay (but rocky) dominant soil.

ʻAmaʻu is a relatively slow-growing fern, certainly slower than ferns like laukahi (Reholttumia hudsoniana), niʻaniʻau (Nephrolepis exaltata subsp. hawaiiensis), and palapalai (Microlepia strigosa). For ʻamaʻu in containers, apply a balanced controlled-release fertilizer with minor elements about every six months, or use a foliar organic or inorganic fertilizer diluted to ⅓ to ½ the recommended strength every couple of months. When applying the controlled-release fertilizer, just sprinkle it on the media's surface and water it in; DO NOT till (i.e., mix) the fertilizer into the media because this can damage the fern's shallow fibrous root system. ʻAmaʻu in the ground don't seem to require fertilization, unless you see poor color (e.g., yellowing fronds) or no growth at all.

At high elevations or high humid sites, ʻamaʻu tolerates windy conditions well. However, in hotter or drier places, strong or frequent winds will likely cause too much evaporation and burn the fronds of your fern. Therefore, choose your planting site wisely or take steps (above) to minimize the temperature and maximize the humidity of your landscape.

Like hāpuʻu (Cibotium chamissoi), ʻamaʻu tends to form a natural skirt of dead fronds at its base. It's your call if you find this feature attractive or ugly. If ugly, remove the old fronds with a hand-pruner, being careful not to damage the fern's trunk or emerging fiddleheads.

Pests and Diseases

I (Koebele) never encountered any pest or disease problems with my ʻamaʻu. However, while I never saw the two-spotted leafhopper (Sophonia rufofascia) on my ferns, you should keep an eye out for this very destructive pest. Refer to the Cibotium chamissoi page for more information on the two-spotted leafhopper.

Wild tree ferns are regularly eaten (because of their starchy pith) and killed by feral pigs. Therefore, if you live near a forested area, remain vigilant of this potential threat, and, maybe, erect some type of barrier around your ʻamaʻu.

Uses

Ancient and Post-contact Hawaiian

Degener [1973] has, perhaps, the most comprehensive description of the many uses Hawaiians had for Sadleria. Below is my (Koebele) summary of his description along with a few additions or clarifications from other sources.

In his description, Degener refers to Sadleria pallida by its synonym S. hillebrandii, which he says Hawaiians called ʻamaʻu. He also states that Hawaiians referred to S. cyatheoides as ʻamaʻumaʻu.

"A generation or two ago," referring to the 1800s, the hair-like scales near the developing fiddleheads of S. cyantheoides, called pulu ʻamaʻu, were harvested, similar to the pulu of Cibotium species, and shipped to California to be used as stuffing for pillows and mattresses. (See Uses;Modern on the Cibotium chamissoi page for a more complete description of the post-contact uses of pulu.)

Hawaiians beat Sadleria frond stalks together with other fiber plants (e.g., wauke, māmaki) to assist in "sizing" when making kapa; "sizing" involved measuring the kapa and creating lines along the edges to permanently record its size. The sap from rolled up fronds, called pepeʻe a palaholo, was used to either moisten kapa or create an adhesive to bind together or repair pieces of kapa [Krauss 1993]. The outer part of the trunk (and the young fronds [Krauss 1993]) were mashed to extract a juice that was then heated to evaporate and concentrate a red pigment used to dye kapa.

Hawaiians would build temporary shelters using Sadleria cyantheoides, which is believed to be the origin of one name for the fire pit within Kīlauea Crater, Halemaʻumaʻu, meaning "the house of the ʻamaʻu."

The starchy pith of Sadleria pallida was cooked in an imu, though not as commonly as hāpu‘u (Cibotium spp.). The young fronds were also eaten.

Hawaiians would cover the ground in drier places with Sadleria pallida and S. cyantheoides fronds. They would then remove the fronds whenever it rained, plant their seeds or cuttings, and re-cover the ground to reduce evaporation.

Both Sadleria cyantheoides and S. pallida fronds were sometimes used for thatching hale whenever pili (Heteropogon contortus) was scarce. The fronds were also used to cover and rainproof the ridge and corners of hale made from pili or other materials. Lastly, Sadleria pallida fronds were placed to cover the ground on the side of a heiau where an ali‘i and his attendants would walk.

Kaʻaiakamanu [1922; 2003] claims ʻamaʻu or ʻāmaʻumaʻu, prepared with other plant parts, was used to "cure asthma and kindred troubles," bring to a head boils, blind pimples, and similar afflictions, and treat palahū (rot) and kaokao ‘ino (syphilis). Krauss [2001] also claims ʻamaʻu was used to treat asthma; however, her prescription differs from that of Kaʻaiakamanu.

Modern

Special Features and Information

General

Blechnaceae contains more than 200 species within 7 to 9 genera. The family occurs nearly worldwide, but is most diverse in the tropical regions of the Southern Hemisphere. Nearly all the species in the family are terrestrial or grow on rocks [Britannica;Blechnaceae].

There are currently (2025) six species of Sadleria in Hawai‘i, all being endemic to the Islands [Flora of the Hawaiian Islands]. The genus can be divided into two groups. (1) The Cyatheoides group are medium-sized to large, even tree-like, ferns found in many habitats from recent lava flows to mesic and wet forests. This group includes: S. cyatheoides, S. pallida, S. souleyetiana, and S. wagneriana. (2) The Squarrosa group are small ferns found on dark, wet banks, and includes S. squarrosa and S. unisora [Palmer 2003].

Sadleria species may be hybridizing within the genus since plants with intermediate characteristics have been found. However, to date (2025), none of these hybrids have been formally named [Palmer 2003].

Sadleria cyatheoides is one of the first plants to appear on fresh lava flows. Later, its decaying fronds provide a place for the germination of seeds from other pioneer species such as ‘ōhi‘a lehua (Metrosideros polymorpha) [Degener 1973].

Pukui & Elbert [1986] state that the ʻamaʻu fern was one of the forms that Kamapua‘a, the pig god, could assume at will. Pukui [1993] also shares the Hawaiian saying, "Hui ka lau o ka ʻamaʻu i uka ka wai o kahawai" translated as, "When the leaves of ʻamaʻu turn toward the upland, it is a sign of flood." In other words, whenever the wind blows the fronds of the ʻamaʻu so they bend toward the mountains, it is also blowing clouds inland, which will ultimately produce rain.

Hawaiian Name

Interestingly, ʻamaʻumaʻu is the plural of ʻamaʻu (i.e., many ʻamaʻu ferns), as well as the name for young ʻamaʻu ferns. It can also mean "ferny," "abounding in ʻamaʻu ferns" or "a covering of ʻamaʻu ferns" (preceded by ke). Puaʻa ʻehuʻehu translates to English as "red pig" [Pukui & Elbert 1986]. Āmaʻumaʻu is a spelling variation of ‘amaʻumaʻu [Kent 1986].

Etymology

Sadleria honors Dr. Joseph Sadler (1791–1849), a Hungarian physician who studied the ferns in his native country [Palmer 2003]. The species name, cyatheoides, means "resembling Cyathea," another tree fern genus [Gledhill 2008].

BPK