Other Hawaiian Rusts of Interest:

Puccinia molokaiensis on Carex sp. (Cyperaceae)

P. molokaiensis was described as a new species upon its discovery in 1928 on the island of Moloka‘i.  It is tentatively considered to have been endemic to Hawai‘i, although no specific, comparative studies involving this rust are known to have been conducted, and it is acknowledged that rusts of tropical Carex hosts have received inadequate attention.  Presently, the site of its collection has been destroyed and no other rust matching the description of P. molokaiensis has been reported from Hawai‘i.  Thus, the rust is thought to be probably extinct.   The only specimens, those of the original collection, are now meager, with teliospores very scarce.  No photographs of the rust are known other than those shown here.  In his discription of the holotype, G. B. Cummins noted the characteristic "large urediospores with thick, aculeate walls"  (Cummins, 1937.   Descriptions of tropical rusts.  Bull. Torrey Bot. Club, 64: 39-44).  The original description did not mention paraphyses, although numerous paraphysis-like structures were found in recent studies of hebarium specimens.

   Urediniospores of P.   molokaiensis.

  A teliospore and numerous paraphysis-like structures of P.   molokaiensis.

Melampsora yoshinagai on Wikstroemia spp.  (akia) (Thymelaeaceae)

The genus Wikstroemia is represented in Hawai‘i by 12 endemic species of small trees and shrubs. Melampsora yoshinagai was originally described by Arthur as Pucciniastrum wikstroemiae, and has since been considered endemic to Hawai‘i (Stevens, 1925) until recently. Because only the uredinial state has been found, the rust was renamed as Uredo wikstroemiae in N. Hiratsuka's monograph of the Pucciniastreae in 1958.  The rust had been collected only rarely since the time of its description until it was found on W. oahuensis in 1987, and still more recent collections have been made on W. uva-ursi (Gardner, 1992, 1994a). Examination of fresh material revealed the presence of prominent captiate paraphyses, apparently not observed previously, that led to the reclassification of the rust as a member of the genus Melampsora.  The rust was referred to M. yoshinagai, a species known on other Melampsora hosts in Japan, Taiwan, India, and the Philippines.  Thus, in its present concept, M. yoshinagai is considered indigenous, rather than endemic to Hawai‘i (Gardner, 1988b).

  Echinulate urediniospores (small arrow) and capitate paraphyses (large arrow) of Melampsora yoshinagai.

Uredo myopori on Myoporum sandwicense  (naio) (Myoporaceae)

Uredo myopori has been found only on the island of Hawai‘i (the "Big Island") on a few trees of the endemic tree Myoporum sandwicense, also known as naio, or "false sandlewood."  This species is the only representative of the Myoporaceae in Hawai‘i.  The original description of the rust was published by G. B. Cummins in the early 1950s as the only Hawaiian specimen among a miscellaneous group of new collections from other regions of the world on deposit at the Arthur Herbarium, Purdue University.  Consequently, the description of the new Hawaiian species was overlooked until the rust was rediscovered in 1989 (Gardner, 1989).   In his description, Cummins stated that U. myopori and Aecidium myopori, from New Zealand, were the only rusts recorded on the Myoporaceae.

  Uredinia of Uredo myopori on the undersurfaces of leaves of Myoporum sandwicense.   Rust-infected areas of the leaf are often red-pigmented.

  Urediniospores of Uredo myopori.

Uredo vulcani on Coprosma spp.  (pilo) (Rubiaceae)

Uredo vulcani was described in 1988 on Coprosma rhynchocarpa, a small tree endemic to the island of Hawai‘i (Gardner, 1988b).  The rust was inconspicuous, occurring as scattered or clustered minute yellow uredinia on leaf undersurfaces of the few individual trees that appeared to be susceptible to infection.   It was found only in Kipuka Puaulu, Hawai‘i Volcanoes National Park.  More recently, this rust was found on C. waimeae, a host endemic to the island of Kaua‘i.  Currently, therefore, U. vulcani is known only from highly localized and disjunct areas of the two most widely separated major islands.  There is little doubt that the rust occurs on Coprosma hosts at other sites as well but has been overlooked because of its inconspicuous appearance.

   Uredinia of Uredo vulcani on a leaf undersurface of the Coprosma host.

  Although not a characteristic unique to this species, urediniospores of Uredo vulcani are characteristically echinulate, but with smooth regions on the spore surface.

Uredinopsis hashiokai on Pteridium aquilinum (bracken fern) (Hypolepidaceae)

This fern host previously was referred to as Pteridium aquilinum, the bracken of worldwide distribution.  Recently, however, the Hawaiian bracken has been recognized as an endemic subspecies (P. aquilinum subsp. decompositum), or has been elevated to endemic species status, distinct from P. aquilinum, as P. decompositum (Gardner and Flynn, 1996; H. Wagner, personnal communication).  The rust uredinia are found on the lower surfaces of fronds and are distinctive in that the urediniospores are completely devoid of pigment, thus appearing white.  When mature, the masses of white spores are observed beneath the prominently ruptured epidermal covering of the uredinia.  The white spores are easily distinguished from other rust fungi and also from the fern spores with which they might otherwise be confused.  The lack of pigmentation is sometimes considered a primitive characteristic and, together with its occurrence on a primitive vascular host, is taken as evidence that the rust and the fern host have had a long, close evolutionary history together.  Where it occurs elsewhere, U. hashiokai has species of fir as its alternate host, upon which the spermogonial and aecial states are produced.   Infection on fir hosts may be so severe that the rust may cause economic losses on these timber species.  However, the alternate host does not occur in Hawai‘i (Hawai‘i has no native gymnosperms) and only the uredinial state has been found to date.  In the absence of the telial state, characteristics of the spore wall ornamentation of the urediniospores within the genus Uredinopsis are used in species identification.  Urediniopsis hashiokai is characterized by rows of tubercles arranged linearly on the spore surface.

   Urediniospores of Urediniopsis hashiokai.  Note the linear, ridge-like arrangement of tubercles on the spore surface.

Puccinia heterospora on Sida spp. and Abutilon spp.

Several native (indigenous or endemic) members of the Malvaceae in Hawai‘i are hosts of Puccinia heterospora, a nonnative rust probably introduced on weedy malvaceous hosts which has now become established on native species.  Infection is often heavy and conspicuous, producing prominently dark blotch-like telia on the leaf undersurfaces, and corresponding sharply defined yellow spots on the upper surfaces.

  Telia of Puccinia heterospora on the lower surface of a leaf of Sida fallax (ilima).  This rust does not produce uredinia.

  Chlorotic spots on the upper surface of the P. heterospora-infected leaf.

References