Last Addition: April 21, 2006
Each "thumbnail" image below is linked to a larger photograph.
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Once much more plentiful and with a wide distribution around the upper flanks of Mauna Kea, the only known remaining natural population of this silversword consists of a few individuals on precipitous cliffs in the upper Wailuku River drainage (photo 1987). These sites afforded some protection from the herbivorous mammals that decimated the species. |
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Silversword morphometrician Alain Meyrat sizes up one of the last remaining naturally occurring individuals of its kind (photo 1977). |
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For several years the State of Hawaii sponsored efforts to grow Mauna Kea silverswords in cultivation and out-plant them in an exclosure in the vicinity of the last remaining natural population. Many of these plants, derived from seedlings such as the one pictured here, survived to flowering maturity when out-planted. A large proportion of the out-plants, like this seedling, were branched, and continued to flower over several seasons, with each branch flowering and subsequently dying back to the main axis independently of others. The branching and subsequent flowering behavior may be due to the effect of greenhouse cultivation during early seedling development but also could be related to the fact that one, or at most, two female parents produced all of the seeds used in these early efforts of propagating the species. Thus, what appears to be a higher rate of polycarpy in the out-plants compared to naturally occurring individuals (and Haleakala silverswords) may be the result of inadvertent artificial selection for this trait. Current recovery efforts with this species are based on knowledge of genetic variation in the small natural population. Progeny resulting from controlled crosses between genetically divergent parents have been used in an extremely successful out-planting program with more than 3000 plants at several locations around the flanks of Mauna Kea. These efforts have been the result of collaboration between the Silversword Foundation (robichau@u.arizona.edu) and local conservation agencies. |
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This is an out-planted individual flowering in an exclosure in the vicinity of the natural population. It is branched and has at least three other rosettes that may flower in future years. (photo 1978) |
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This out-plant had two rosettes that flowered in a previous year, one flowering when the photo was taken and one that remained to potentially flower in a future year. The bright green foliage just below center on the left edge of the photo is another member of the silversword alliance, Dubautia arborea. The two species are known to hybridize spontaneously. (photo 1987) |
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This is a highly branched out-plant with three flowering rosettes and several vegetative rosettes that potentially would flower in future years. In case you didn't recognize him in shorts, that is Bruce Baldwin (Curly) on the right. The Mauna Kea silversword tends to differ from the Haleakala silversword in having a longer, narrower flowering stalk, fewer ray flowers, and longer, narrower, and straighter leaves. (photo 1987) |
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Another attractive branched out-plant (1997). |
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Inflorescence of one of the out-plants flowering in 1997. |
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Though the flowering heads of the Mauna Kea silversword can be somewhat larger and darker colored than the one pictured here, they tend to be smaller and have fewer ray flowers than those of the Haleakala silversword. Receptacular bracts are usually restricted to the periphery in most heads of silverswords, but occasional heads such as this display a few bracts towards the center of the disk. Prominent glandular hairs on the herbage have sticky secretions similar to mainland relatives that are called tarweeds because of the gooey exudates they produce. (photo 1977 - from plant cultivated at Hawaii Volcanoes National Park) |
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More glandular hairs are visible in this side view of a flowering head. Also apparent are peripheral receptacular bracts inside the ray flowers and involucral bracts that subtend them. (photo 1977 - from plant cultivated at Hawaii Volcanoes National Park) |
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View of portion of head from plant flowering in 1997. Visible here are two Lygaeid bugs, perhaps the endemic Nysius terrestris. |