Floridata Article

Iliau-Kaua`i's Silversword

Wilkesia gymnoxiphium
Photo 1 - Wilkesia gymnoxiphium on the iliau Loop Trail with the Waimea Canyon in the background.

In an earlier article, I talked about the Hawaiian Islands’ most widely advertised plant-what I called the Flagship Plant of the Islands-the silversword. In addition to the four or five species (one may be extinct) of Argyroxiphium, the commonly termed “silversword alliance” encompasses two other genera, Wilkesia, to be described here, and Dubautia, which will be dealt with later in an article of its own. The genus Wilkesia consists of two species, both of which are restricted to western Kaua‘i. One of these is very easy to see in the wild; the other presents a more formidable challenge. Let's look at the easy one first.

Wilkesia gymnoxiphium
Photo 2 - Multi-headed or candelabra form of W. gymnoxiphium
Wilkesia gymnoxiphium
Photo 3 - Close-up of glands of Wilkesia gymnoxipium
Wilkesia gymnoxiphium
Photo 4 - Close-up of a composite head of W. gymnoxiphium

Iliau, the Hawaiian name for the larger of the two species, was first observed by non-Hawaiian botanists from the United States Exploring Expedition of 1838-1842. Material of iliau was delivered to Asa Gray, Professor of Botany at Harvard University, who named the new genus Wilkesia after Captain Charles Wilkes, the leader of the expedition. The specific epithet, gymnoxiphium, refers to the plant’s leaves and is based on the Greek root “gymno-” meaning naked and “xiph-“ meaning sword-like. Unlike the Big Island and Haleakala silverswords, which have a rosette of leaves out of which the flower structure emerges, iliau leaves emerge from the top of a stalk. Eventually, the flowering structure emerges from the center of the tuft of leaves. Photo 1 features a typical plant with a single flowering head with the Waimea Canyon as a backdrop. The equally common multi-head or candelabra-like form of the plant can be seen in Photo 2. Details of the glands and individual composite flower head are shown in Photos 3 and 4, respectively.

Populations of iliau occur along the western rim of Waimea Canyon and on several of the ridges that radiate from the canyon rim. A population (Photo 5) can be found at the Y-junction of Highways 550 and 552 (where there is a convenient, although unmarked, parking area). A much larger population occurs a few miles further north along the highway (with a much smaller parking area) that features the Iliau Loop Trail. Unfortunately, this site is poorly signed but can be found by looking for the hiking trail marker announcing the Kukui Trail, which provides access to the canyon. A shelter with picnic table is provided. The Iliau Loop Trail encompasses an area of several acres bordered by the canyon rim on the east. Flowering occurs mostly during the summer with only dead flower stalks visible during the winter.

Wilkesia gymnoxiphium
Photo 5 - A population of W. gymnoxiphium at the junction of Highways 550 and 552.
Wilkesia gymnoxiphium
Photo 6 - The author with W. gymnoxiphium plants. Note very early flower head development. Photo by M. H. Hawkes
Wilkesia gymnoxiphium
Photo 7 - Developing flower head of W. gymnoxiphium, early stage.
Wilkesia gymnoxiphium
Photo 8 - Developing flower head of W. gymnoxiphium, later stage.
Iliau is described as a monocarpic species, meaning that once it flowers and sets seeds, it dies. Like the silverswords, iliau plants may take 20 years or more to reach reproductive maturity.

The development of the flowering head is a fascinating process to observe starting with the appearance of a large bud-like structure-like a very large spear of asparagus-followed by opening of rank after rank of individual composite heads themselves. This sequence is illustrated in Photos 6, 7, and 8.

The ease of seeing iliau in Nature is contrasted by the difficulty of finding the other Wilkesia species, W. hobdyi, known commonly as the dwarf iliau (Photo 9). This species entered the list of Hawaiian endemics much more recently; it was formally described in 1971 based on specimens collected in 1968 at the tip of Polihale Ridge by Robert Hobdy (retired botanist and forester). The specific epithet “hobdyi” recognizes his contribution.

The plants occur on very dry ridges overlooking the Pacific Ocean on Polihali Ridge (Photo 10) and adjacent Ka‘aweiki Ridge. The sites are difficult to access and very dangerous to explore, as the plants grow on crumbly substrate on steep hillsides (Photo 11). One ill-chosen foot hold could result in a very speedy descent that might end up in the ocean-if the faller happened to be lucky.

Only about 350 individuals were thought to exist according to a 1985 estimate (I have no information on how many plants may still exist). The area is frequented by goats, who we heard but didn't see on our visits. These animals are doubly threatening because of their indiscriminate dining habits, as well as their capacity to destroy the plant‘s habitat. In addition to being smaller, the dwarf iliau differs from its larger relative by being polycarpic, in reference to the fact that it does not die after flowering and setting seed.

Wilkesia hobdy
Photo 9. Dwarf iliau, Wilkesia hobdyi, site on steep slope of Polihale Ridge.
Wilkesia hobdy
Photo 10. A view of Polihale Ridge. Dwarf iliau grows just over the brow of the ridge. Barking Sands Beach is in the background.
Wilkesia hobdy
Photo 11. The author examining a specimen of dwarf iliau on Polihale Ridge. The Pacific Ocean beckons 1500' below.

A few comments on the origin of the generic name Wilkesia may be of interest. The contributions of many famous biologists have been recognized in naming of organisms throughout the history of biology. The Latinized name of Karl von LinnĂ© (Linneus)-often called the father of taxonomic nomenclature-is memorialized in the name of the circumboreal twinflower Linnaea borealis, reputed to have been his favorite plant. Darwinia is a genus in the Myrtaceae (eucalypt family); the geneticist Darlington is remembered in the name of the carnivorous Darlingtonia californica of the Sarraceniaceae. We also find Davidia, Davidiaceae, Davidsonia, and Davidsoniaceae. Readers familiar with ferns may recognize Dicksonia, one of the tropical tree fern genera. One could go on but let's get back to Hawai‘i. Several Hawaiian botanists have been honored, an example of which we saw above with Robert Hobdy. Other examples include Hillebrandia sandwicensis (monotypic Hawaiian endemic genus in the Begoniaceae) which recognizes Wilhelm Hillebrand who collected widely in the islands (1851-1871) and wrote the Flora of the Hawaiian Islands. There is also Hibiscus kokio subsp. saintjohnianus, the subspecific form named in honor of Harold St. John, Professor of Botany at the University of Hawai`i. The majority of folks commemorated in this way have made noteworthy contributions. The recognition of Captain Charles Wilkes by Asa Gray likely seemed at the time to be another instance of honoring a significant contributor. The end of the story is quite the opposite. Wilkes’ military career ended in the disgrace of a court-martial, where he was described as “.violent, overbearing, and insulting; incoherent and rude; and offensive in the highest degree.” Other terms used to describe him included “.crass, foolish, and inept.” The full tale can be found in an article by D. R. Stoddart in Darwin's Laboratory edited by R. MacLeod and P. F. Rehbock, University of Hawaii Press. It is well worth the read.

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