Floridata: Hawaiian Silverswords

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The Hawaiian Silverswords
Flagship Plants of the Islands

by Bruce A. Bohm

Photo 1: Haleakala silverswords in the crater

Photo 2: Mauna Kea silverswords in full flower.

Of all the spectacular plants that occur naturally on the Hawaiian Islands, none is more impressive than the silversword Photos 1-3. More pictures have been taken and words written about them than any other plants on the islands; they are at the top of most plant lovers' must-see lists. Brought to the brink of extinction by habitat destruction and the dining habits of introduced animals - cattle, sheep, goats, and pigs - the 'swords are being coaxed back into life through a program of reintroduction, in the case of the Mauna Kea plants, and an extensive fencing effort designed to protect the plants on Haleakala.

The first European to collect specimens of silverswords was James Macrae, who was part of a small party to visit the summit of Mauna Kea in 1825. Macrae, botanist on board the H. M. S. Blonde, recorded in his journal, a bit understated perhaps, that the plant is “...truly superb, and almost worth the journey of coming here to see it on purpose.” His specimens eventually found their way back to Europe where they were studied and given the formal name by which they are now known. A few years later silverswords were discovered on the flanks and in the crater of Haleakala, the dormant volcano that dominates East Maui.

Photo 3: Close-up of a single composite flower head of the Mauna Kea silversword.

Photo 4: Leaves of the silversword showing their reflective surface.

Photo 5: Flowering head developing.

Collectively, these plants are known as Argyroxiphium sandwicense, the generic name being derived from the Greek “argyros”,in reference to the silver appearance of the leaves and “xiphium”, the word for dagger. The long, soft hairs on the leaves (Photo 4) that give the silvery appearance serve two important functions: they reflect much of the intense sunlight that falls on these plants at the high elevations where they live - at about 8,000-10,000 ft (2440-3050 m) - and they break up air flow over the surface of the leaves, thus reducing excess evaporative water loss. The specific epithet ‘sandwicense’ is derived from the Sandwich Islands, the name given to the islands by Captain James Cook on his third visit in recognition of the support provided by his friend John Montague, 4th Earl of Sandwich and first Lord of the Admiralty.

Plants from the two islands were treated pretty much as identical by most people, although some suggested that the flower heads of the Haleakala plants were a bit different. Recently this question was revisited by botanists at the University of Hawai‘i at Manoa who examined the flowering structures of plants from both sites and concluded that differences between the two were sufficient to recognize the Haleakala plants as a separate subspecies. Because the flowering heads of the Haleakala plants are bigger than those on Mauna Kea, the new name assigned was A. sandwicense subsp. macrocephalum (macro = large, cephalum = head). As required by the rules of botanical nomenclature, the original plants-the ones on Mauna Kea-must be named A. sandwicense subsp. sandwicense. Differences in geographic distribution, along with appropriate structural differences of course, are often recognized at the subspecies level.

The easiest way to see a Mauna Kea silversword is to visit the Hale Pohaku (literally, House of Stone) Ranger Station at 9,200 ft (2805 m) on the southern flank of Mauna Kea (uphill from the Saddle Road-Summit Road junction). The station's parking lot serves as the starting point for convoys to the astronomical observatories on the summit (four wheel-drive vehicles only!) The station has a small museum and a gift shop, several telescopes on display, and behind the parking lot, a small fenced silversword garden.

Photo 6: Emerging floret in silversword head. Note glands.

Photo 7: Silversword seedlings in the nursery.

It is much more difficult to see the Mauna Kea silverswords in their native habitat. A wire fence exclosure on the eastern flank of the mountain at about 9,000 ft (2740 m) is home to a population of 'swords. These out-planted individuals can only be reached by way of an extremely rough track (definitely not a road!) followed by an uphill hike. Visits to this area should only be attempted in the company of an experienced person. The fortunate visitor, however, may be rewarded with views of plants in full flower, or beginning to develop their flower heads as seen in Photo 5. Photo 6 shows the very first ray florets beginning to emerge. This picture is also a good chance to observe the glands, which contain a mixture of sticky chemicals much akin to the gluey material that characterize the tarweeds of western North America, to which the silverswords are closely related.

Before the introduction of cattle and other animals, silverswords grew in a band around the mountain between about 8,000 and 12,000 ft elevation (2440-3660 m) - the summit of Mauna Kea is 13,796 ft (4205 m). Except for a very few places that the animals couldn't reach, silverswords were eliminated from the mountain. In addition to establishing the fenced site mentioned above, a successful program to re-establish populations of these plants at other sites on the mountain is underway. The program has been remarkably successful with nursery-grown seedlings Photo 7 taking very nicely to their new home on the lava hillside Photo 8. Sheep are still a problem but populations are kept in check, more or less, by aggressive hunting.

Photo 8: Out-planted M. Kea silversword.

Photo 9: Haleakala silverswords in the crater.

The situation with the Haleakala silversword isn't quite as dire, although there was a bad spell when destructively motivated people took pleasure at rolling the mature flower heads down steep hillsides. Haleakala silverswords are maintained in a garden display near the entrance to the National Park Center.

Flowering occurs during the summer months, but since these plants only flower once in their lifetime (and then die) it is a bit of a lottery to see one of the display plants in bloom. A few plants are also maintained in a small garden at the summit parking lot of the mountain at about 10,000 ft (3050 m). In order to see the Haleakala silversword in its native habitat, however, visitors must hike into the crater on the Shifting Sands Trail to the Silversword Loop Trail area. If hiking back up at that elevation (down is never a problem) isn't to a visitor's liking, it is possible to do it on horseback; a local trail outfitter offers the service. Photos 1 and 9 feature the Haleakala plants and give an idea of the stunning scenery of which they are part.

For more on this topic click to read Bruce's article Hawaiian Lava Life

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