Sunday, August 29, 2010

Forest Quote

Although it is composed of trees, the forest is far more than a collection of trees standing in one place. It has a population of animals and plants peculiar to itself, a soil largely of its own making, and a climate different in many ways from that of the open country. Its influence upon the streams alone makes farming possible in many regions, and everywhere it tends to prevent floods and drought. It supplies fuel, one of the first necessaries of life, and lumber, the raw material, without which cities, railroads, and all the great achievements of material progress would have been either long delayed or wholly impossible.
– Gifford Pinchot

Dodonaea viscosa – Varnish Leaf

Plant in flower. © 2007 by Forest and Kim Starr. Used under a Creative Commons license.

Dodonaea is a small genus of approximately 70 species of woody shrubs or small trees with alternate (or rarely opposite) simple or pinnate leaves. About 60 species are confined to Australia, about nine more occur in Africa, the Americas, and Asia, and one species, Dodonaea viscosa, is pantropical and occurs as a native plant on all continents except Antarctica and Europe. In Florida, Dodonaea viscosa is known as varnish leaf, a reference to the shiny, sometimes sticky, resinous coating on the leaves. It is remarkablly adapted to harsh coastal environments where it tolerates moderate salt spray, wind-blown sand, strong winds, and intense sunlight. Although usually growing as a small shrub up to 3 meters (10 feet) tall, in Hawaiian forests it is sometimes a tree up to 9 meters (30 feet) tall. Varnish leaf is characterized by alternate, simple, elliptic-shaped leaves; greenish flowers that are mostly either male or female on separate plants; and inflated, papery, 3-celled and 3-winged capsules that hold a few rounded, black seeds. The capsules are green when young, changing first to pale green and then gradually to various shades of pink, red, brick red, or purplish red, and eventually to light brown at maturity. Depending on growing conditions, temperature, and the plant's genetic background, the reddish color can be intense and may produce a highly ornamental effect.

Dodonaea viscosa is remarkable for its fast growth, general freedom from pests and diseases, and ability to thrive under highly varied conditions. In Florida, it is restricted to coastal strand and coastal hammocks but elsewhere in its range it grows in extremely diverse habitats. For example, in Hawaii it is found in "coastal dunes, lava fields, [and] dry, mesic and wet forests" (Anonymous 2009). Its altitudinal range in Hawaii is as impressive as the variety of habitats in which it occurs and it can be found in lowlands at 3 meters (10 feet) of elevation all the way up to subalpine shrubland at 2,347 meters (7,700 feet) (Little & Skolmen 1989). In the United States, in addition to to Florida, it occurs as a native plant in Arizona where it is described as "fairly common on dry, rocky slopes and in canyons, often on limestone" (Kearney & Peebles 1951:528). In California, it has been recorded from Orange County (USDA, NRCS 2010).

Drawing from Little & Skolmen 1989, a U.S. Government work (as republished by the University of Hawaii at Manoa 2003).

Varnish leaf is easily grown from seeds, although patience is required since germination rates may vary from a few weeks to several months. Propgation may also be effected from shoots with half-ripe wood taken in the summer (Plants for a Future 2010). Due to its rapid growth and ease of cultivation, varnish leaf is highly recommended for beginning gardeners in USDA plant hardiness zones 9–11 and it can generally be expected to succeed so long as it is provided sufficient water during establishment and is situated in an area with ample sunshine and well-drained soil. It is admirably suited for coastal gardens where many other plants find life difficult but it will also grow well inland. Due to its fast growth, evergreen leaves, and tendency to freely branch, it is perhaps most often used as a hedge or screen but it may also be profitably grown as a specimen plant, foundation plant, and in coastal and tropical hammock restorations. In addition to the wild form with bright green leaves, there is a popular purple-leaved cultivar that is extensively cultivated in the United States; however, plants of this cultivar that I saw in San Francisco seemed less vigorous than the green-leaved plants I am familiar with in Florida. Varnish leaf has very few faults only two of which are fairly serious. Occasional plants may become black from mildew growing on the sugary secretions of mealy bugs and scale but this situation is easily remedied by cutting the plant to the ground, after which it soon sprouts new, pest-free shoots that can attain their former height within a year. Another problem is that plants can become a big, floppy messs if provided with too much water or if planted in very rich soil.

Besides it ornamental uses, varnish leaf has numerous medicinal uses although such practices are not recommended since the leaves contain cyanogenic compounds, tannins, and saponins, all of which are toxic in sufficiently high quantities. The conspicuous capsules are both reminiscent of hops and have been used as a substitute for hops to add a bitter flavor to beer, thus accounting for another of its common names, hop bush. It is of considerable biogeographic interest in that it "and wingleaf soapberry ... Sapindus saponaria, are the only tree species native in both Hawaii and continental United States" (Little & Skolmen 1989).


  • Anonymous. 2009. Native Plants of Hawaii: Dodonaea viscosa. University of Hawaii. Internet
  • Kearney, T.H. and R.H. Peebles. 1951. Arizona Flora. Berkeley and Los Angeles: University of California Press.
  • Little, Jr., E.L. and R.G. Skolmen. 1989. Common Forest Trees of Hawaii (Native and Introduced). Agriculture Handbook No. 679. Forest Service, United States Department of Agriculture (as republished by the University of Hawaii at Manoa, 2003). Internet
  • Plants for a Future. 2010. Dodonaea viscosa. Internet
  • USDA, NRCS. 2010. The PLANTS Database (, 29 August 2010). Baton Rouge: National Plant Data Center. Internet

© 2010, except as noted, by Rufino Osorio.

Harrisia fragrans – Fragrant Prickly-Apple

Harrisia fragrans is a rare, federally-listed endangered cactus of sandy coastal areas and recorded from Volusia, Brevard, Indian River, and St. Lucie counties along the east coast of peninsular Florida. It is now extremely rare in the wild and it has been reduced to approximately 320 plants in St. Lucie County (Possley 2010), with all other occurrences having been eliminated as a result of habitat destruction. The prospects for this plant appear dim since the wild populations show high death rates for mature plants and low rates of recruitment and establishment for seedlings (Rae & Ebert 2002).

The plant is characterized by narrowly columnar stems with 10–12 ribs and growing 3–5 meters (9.8–16.4 feet) long. Such lengths appear to be the result of plants trying to grow above the surrounding vegetation since cultivated plants in full sun tend to remain much shorter. Young shoots are very showy as a result of the bright yellow spines that contrast beautifully with the dark green stems. The spines darken as they age but even on very old stems, the spines will usually retain yellow tips.

Disproportionately large, fragrant, white flowers are produced in late spring and these quickly develop into huge, rounded, orange-red fruits that take several months to ripen. The fruits are sparsely covered with small scales and are filled with numerous seeds embedded in a mildly sweet white flesh with a pleasing flavor. Fruits can be cut in half and the flesh and seeds scooped out and eaten in the same manner as kiwi fruits and, like kiwi fruits, the flavor can be enhanced by adding a squeeze or two of lime. Plants are equally ornamental in flower and in fruit and the latter are "a great attraction as food for birds, many of whom are ravenously fond of the seeds" (Small 1932 quoted in Parfitt & Gibson 2003).

Harrisia fragrans is very easily cultivated from seeds and young plants about two years old and only 30.5 centimeters (12 inches) tall will readily flower and set fruit in a small pot. Plants are also easily propagated by stem cuttings that have had their cut ends allowed to dry for a day or two and then inserted into sandy soil. If one has the room, it should be grown in large groups where quantities of large white flowers will present a very attractive sight and many fruits can be produced, to the gastronomic delight of the gardener, assorted mammals, and birds.

Harrisia fragrans, under the name Cereus eriophorus var. fragrans, was formerly treated as a variety of Harrisia eriophorus; however, the latter is now regarded as an exclusively Caribbean species that differs in its 8–9-ribbed stems and longer, black-tipped spines (Parfitt & Gibson 2003).


  • Britton, N.L. and J.N. Rose. 1920. The Cactaceae: Descriptions and Illustrations of the Cactus Family. Volume II. Washington, D.C.: Carnegie Institution of Washington Publication No. 248. Internet
  • Parfitt, B.D. and A.C. Gibson. 2003. Harrisia. pp. 152–153. In Flora of North America Editorial Committee (eds.) Flora of North America: Volume 4. New York: Oxford University Press. Internet
  • Possley, J. 2010. CPC National Collection Plant Profile: Cereus eriophorus var. fragrans. St. Louis: Center for Plant Conservation. Internet
  • Rae, J.G. and T.A. Ebert. 2002. Demography of the Endangered Fragrant Prickly Apple Cactus, Harrisia fragrans [abstract]. International Journal of Plant Sciences 163(4): 631–640. Internet
  • Small, J. K. 1932. Harrisia fragrans—fragrant prickly-apple. Addisonia 17: 29–30.

A plant that survived hurricanes Frances and Jeanne in 2004 produces new shoots in the spring of 2005.

Image published prior to 1923 (Britton & Rose) and now in the public domain. Text © 2010 Rufino Osorio.

Saturday, August 28, 2010

Centaurea scabiosa – Greater Knapweed

Warning: Centaurea scabiosa has a high potential of becoming an invasive pest plant. It is included here only as an aid to identification and not to promote its cultivation in any way whatsoever.

Centaurea scabiosa Linnaeus is native to Siberia and Europe (USDA, ARS 2010) and is distinguished by its deeply lobed leaves and flower heads borne singly at the ends of the stems. The flower heads are subtended by broad, usually pinkish or purplish bracts with the margins fringed at the apex. The outer florets in each flower head are spreading, enlarged, and neuter (that is, sterile and not producing seeds). The plant is a perennial with thick, woody rootstocks that form a large, conspicuous rosette of leaves early in the year and from which arise flowering stems 1–3-feet tall, with the flowers present from July to August or September. Within its natural range, it favors chalky or limestone soils and the image above was taken by John Jordan in "south-west England on the edge of Salisbury Plain, a chalky hillside which used to be grazed pasture many years ago, but is now common land trimmed once a year." Ecologically, it is notable for attracting a wide variety of nectar- and pollen-seeking insects; as the sole source of food for the caterpillars of the case-bearing moth, Coleophora didymella Chr├ętien; and, in Britain, it is usually the only host of the parasitic plant, knapweed broomrape (Orobanche elatior Sutton) (Rumsey & Jury 1991:267). Besides greater knapweed, the plant is also known as greater centaury, hardhead, and ironhead, the latter two common names being a reference to the hard, solid flower heads (Grieve 1971:456).

Greater knapweed is now well established in Canada and throughout a wide range in the northern United States. Although it is definitely weedy, it is not currently listed as ecologically invasive in North America; however, due to the tendency of Centaurea species to become invasive pest plants in the northern United States and Canada, its cultivation should not be encouraged and plants growing in the proximity of natural areas should be closely observed and eliminated if seen to be spreading at the expense of the native flora. Greater knapweed might be mistaken for spotted knapweed, Centaurea stoebe L. ssp. micranthos (Gugler) Hayek (Centaurea maculosa auct. non Lam.), which is an invasive pest plant, since both plants have deeply lobed leaves. However, the latter has much smaller flower heads up to 1-inch wide, whereas greater knapweed has larger flower heads that are 2 inches wide or wider.

Observant readers may have noticed the red-spotted black moth at the base of the flower head. It is a burnet moth in the genus Zygaena, a group of day-flying moths that sequester cyanogenic glucosides from various members of the pea family that serve as food for the caterpillars, although George (2010) reports that these moths can also manufacture cyanogenic glucosides and do not need to obtain them from the larval food plants. The boldly patterened wings are an example of aposematic coloration, which is also known as warning coloration and serves as a visual cue to predators that the moth is distasteful and toxic.

USDA Distribution Map


  • George, H. 2010. Insects That Make Cyanide. Internet
  • Grieve, M. 1971. A Modern Herbal, Volume 2. Mineola, New York: Dover Publications. Internet
  • Rumsey, J. and S.L. Jury. 1991. An account of Orobanche L. in Britain and Ireland. Watsonia 18:257–295. Internet
  • USDA, ARS, National Genetic Resources Program. 2010. Germplasm Resources Information Network (GRIN) Online Database. National Germplasm Resources Laboratory, Beltsville, Maryland. Internet

Image © 2010 by John Jordan and used by permission. Text © 2010 by Rufino Osorio.

Where Can I Obtain Florida Native Plants?

I am frequently asked where one may obtain Florida native plants. So, I thought it was about time I provided a detailed answer. If you would like to know my "secret" sources, go over to the Florida Native Plant Society's blog where I have written a post on sources for Florida native plants.

Monday, August 16, 2010

Hypoxis decumbens

Hypoxis decumbens is a grassy plant that bears small, brilliant yellow flowers. It is easily grown from seed and the plant in the above image was grown to full maturity in a small 2-inch (5-cm) plastic cup in an east-facing window.

It is native throughout a very wide range in Mexico, Central America, the Greater and Lesser Antilles, and South America.

© 2010 Rufino Osorio.

Ludwigia maritima

Ludwigia maritima is a perennial wildflower found in all coastal states from Louisiana to North Carolina. It occurs in flatwoods, bogs, and swamps but, as far as I can tell, it has no connection whatsoever to the sea or to maritime habitats and its species epithet, maritima, which means of the sea, is a bit of a mystery. It is very common in Florida, where it has been recorded from every county except Gadsden, Gulf, Indian River, Lafayette, Monroe, Pinellas, Santa Rosa, Suwannee, and Washington counties. Like many other native herbaceous wildflowers, it is almost unknown in cultivation in spite of being a remarkably graceful plant with slender branching stems that bear showy flowers over a very long period of time.

As is typical of Ludwigia species, it is extremely easy to grow and plants will flower during their first year when grown from seeds. Its cultural requirements are modest and it will happily grow in a pot or in the ground so long as it is provided with moist soil, bright light, and freedom from taller plants. Although adapted to wet soils, the stems arise from deep-seated subterranean tubers and, if subjected to drought, the plant will go dormant and come back from the tubers when conditions improve.


© 2010 Rufino Osorio.

Monday, August 9, 2010

Asimina reticulata

The pineland pawpaws were magnificent this year and many plants were covered with flowers. This one was growing in a sand scrub nature preserve right smack in the middle of urban coastal south Florida approximately 10 minutes from my house by car.

© 2010 Rufino Osorio.

Sunday, August 8, 2010

Ant dispersal in Aristolochia serpentaria (Virginia snakeroot)

Aristolochia serpentaria - Virginia Snakeroot

Myrmecochory, the dispersal of seeds by ants, is a common adaptation among perennials growing in mesic forests, and the principal characteristic of seeds dispersed by ants is the development of the elaiosome, an oily, nutritive appendage that is attractive to ants. Allard (2002:4) reported that the seeds of Aristolochia serpentaria did not exhibit any specialized adaptations for dispersal and that they lacked an elaiosome. However, neither statement is correct as is indicated in the above photograph of a recently opened capsule of Aristolochia serpentaria. Note that the seeds are attractive to ants and that each seed is provided with a large, creamy-white, fleshy elaiosome. Although seemingly small relative to the size of the seeds, these ants were eventually able to remove all but one of the seeds from the capsule.

Dried Aristolochia serpentaria seeds, as might appear on an herbarium sheet, do not display signs of an elaiosome, which in this case quickly dries and shrivels up. It is thus easy to conclude that Aristolochia serpentaria is not adapted for dispersal by ants; however, the cultivation of this plant in pots, which makes very close observation possible, reveals myrmecochory and adds Aristolochia serpentaria to the long list of forest wildflowers with ant-dispersed seeds.


Allard, D.J. 2002. Aristolochia serpentaria L. (Virginia Snakeroot) Conservation and Research Plan for New England. Framingham, Massachusetts: New England Wild Flower Societ. Retrieved on 8 August 2010 from

© 2010 Rufino Osorio.

Sunday, August 1, 2010

Opuntia abjecta

Opuntia abjecta

Opuntia abjecta

Note: This article was originally titled Opuntia triacanthos; however, molecular genetic analysis by L.C. Majure (2012) indicated that it cannot be O. triacanthos because the Florida plants fall into a separate clade than does O. triacanthos from the Caribbean. Majure's research showed that O. abjecta is a distinct species originally distinguished by John Kunkel Small.

Opuntia abjecta is a Florida state-listed endangered species, under the misapplied name of O. triacanthos, that is remarkable for its small size and it slowly forms low mounds that will cover about two square feet and reach 3–6 inches in height in a few years. Previously, Florida's population was thought to be an outlier of the Caribbean species, O. triacanthos. But it is now known to be a distinct species, first recognized by John Kunkel Small, that is endemic to the Monroe County Keys.

Opuntia abjecta

The pads are very weakly attached to one another and this, in combination with the barbed spines, means that they will almost leap onto the shoes, clothing, or fur of anyone or anything that brushes against the plant. Thus, it should not be situated where animals or people will pass nearby. This is not only for the benefit of passersby, but for the plant itself since the frequent loss of pads causes the clumps to fall apart and they will not flower as freely as undisturbed clumps.

This interesting miniature succulent is well worth growing in succulent plant collections. If one lacks a garden, it can be grown as a potted plant, and I have flowered it in a 3-inch pot on a south-facing windowsill.

Majure, L.C. 2012. The Evolution and Systematics of the Opuntia humifusa Complex. University of Florida doctoral dissertation. 10 May 2015.

© 2009, 2015 Rufino Osorio. All rights reserved.