As a winter-flowering shrubby tree with bright yellow flowers, it is hard to say anything derogatory about the stunning Eucalyptus erythrocorys F. Muell. (of the myrtle family, Myrtaceae), listed in the horticultural trade as red cap gum or red helmet. Most Californian gardeners know that the evergreen eucalypts are species native to Australia-about 600 species-where this lineage radiated into woodlands, forests, and shrublands ("bush," in Australian vernacular). The aboriginal name for E. erythrocorys is illyarrie, and locals also call this the Bookara gum. Illyarrie is endemic to Western Australia south of the coastal city of Dongara; there it grows on sandy, limestone soils while receiving an annual precipitation equal to that of Los Angeles.
In the wild of Australia, this plant frequently grows as a multi-stemmed shrub form, called mallee. Species of mallee eucalypts are adapted to resprout after fires from a partially exposed lignotuber (a burllike woody base). Our four leaning specimens, less than 3 meters in height, are thriving in a raised bed outside the western fence of the botanical garden, without special care or pruning and, definitely, without fire, and growing with them is the coarse-leaved mallee, E. grossa, also healthy and relatively carefree.
Eucalyptus erythrocorys differs little in foliage from many species of the genus, and like others has adult and juvenile, petiole-bearing leaves. Adult leaves of illyarrie are leathery sclerophylls-tough, thick, and sturdy-and have the same texture as a 4-by-6 note card, which can be snapped without tearing. These glossy green leaf blades are lance-shaped, 2 to 4 cm wide near the base and up to 26 cm in length, sickle-shaped (i.e., falcate), and curved back toward the stem. Leaf arrangement is opposite, occasionally subopposite, along the reddish young stems. In contrast, juvenile leaves are ovate and much shorter, as compared with adult leaves twice as wide and half as long, thinner and not as tough, and with a straight, not curved, axis; these blades are dull green and both surfaces are conspicuously hairy. Juvenile leaves are produced on rapidly elongating suckers with very long stem internodes arising from the lignotuber, and thereafter only adult leaves are produced. Crushing a leaf produces the faint odor of turpentine, because monoterpenes are released and volatilize from the secretory cavities scattered within the middle tissue of the leaf blade. Apparently this is not a species that has enough eucalyptus oil for economic extraction.
The bark also is fairly typical of many gums and mallees that shed bark as flakes. Newly exposed bark is whitish-gray, which oxidizes to light brown.
Flowers are produced from axillary buds, generally as paired lateral inflorescences, each bearing 2 or 3 flowers with strongly ribbed, green ovaries. As in all Myrtaceae, the ovary is inferior and forms a single style from the sunken apex of the ovary. This ovary is similar to those of other large-fruited mallee species from Western Australia. Eucalyptus erythrocorys has exceptionally wide flowers, being squarish in face view and measuring up to 7.5 cm corner to corner. When all 6 flowers from the node are open, the yellow display is dazzling.
The specific epithet erythrocorys means "red helmet," and this refers to the strawberry-colored, biretta-looking, 4-lobed cap (operculum) that forms the top of the flower bud. The cap abscises when the flower opens, and is comprised of fused perianth parts. The red helmet is unique for the genus Eucalyptus and, therefore, this species is distinctive and unmistaken in a genus where identifications can be extremely difficult.
In E. erythrocorys, the colorful red cap contrasts with the green ovary and 1500 bright yellow stamens-among the highest number of all angiosperms. Stamens are attached along the floral disk, most formed in raised puffs at the four corners, opposite four ridges atop the segments (carpels) of the ovary.
Fruits of the red cap gum are woody and massive capsules (4 to 5 cm diameter), bell-shaped, and strongly ridged, and the depressed center of the fruit is glossy red. Dried stamens often persist on the maturing fruits, and fruits eventually open at the top via four splits.
A few years ago our plants of illyarrie were temporarily attacked by red gum lerp insects living on the leaves (Newsletter Fall 1999), but the infestation passed quickly, and no additional lerps have since been observed there, suggesting that the species is moderately resistant. That is good news, because E. erythrocorys is planted occasionally throughout coastal and desert zones of Southern California (>200 mm annual rainfall), and it would be a shame to lose this magnificent eucalypt from the California plant palette.
ARTHUR C. GIBSON, MEMBG Director