Tuesday, September 6, 2016

Asimina triloba (pawpaw)

Pawpaw (Asimina triloba) is one of several plants in Kentucky’s flora representing the northernmost member of an otherwise tropical family. The same can be said for persimmon (Diospyros virginiana, Ebenaceae–Ebony Family), yellow passion flower (Passiflora lutea, Passifloraceae–Passion flower Family), and prickly ash (Zanthoxylum americanum, Rutaceae–Citrus Family). In pawpaw (Annonaceae–Custard Apple Family), we have a tree that is especially exotic in appearance and even more of a temperate-curiosity because of its tropical-flavored fruits.

Pawpaw is best known because of its fruit, which is the largest edible tree-fruit in the United States. The taste and texture is often described as a cross between banana and mango. Unfortunately, the fruits have virtually no shelf life, and as a result they have not gained wider popularity as a hand fruit. Breeding programs have long tried to produce a more marketable variety: pleasant taste, seedlessness, and a thick ‘husk’ for storage and shipping. 

Pawpaw is extremely common in Kentucky, and autumn is an excellent time to find ripe fruits while hiking. Most frequently found in bottomlands and floodplains with rich soils, the plants tend to form dense colonies by sending up ‘suckers’ from the root system giving the appearance of a thicket of small trees. Asimina belong to one of the more primitive groups of flowering plants and is closely related to Magnolia. Like Magnolia, their leaves are large, simple, entire, and alternate, making them quite easy to distinguish in the wild. Also like Magnolia, the evolution of pawpaw occurred long before that of bees, thus pollination is generally carried out by flies and beetles that are attracted to the floral bouquet of rotting meat. Individual flowers are rust-purple in color and borne very early in spring before the leaves emerge.

Cultivation of pawpaw is easy, provided soils are not overly dry. They can handle both full sun and deep shade, however the latter will generally yield less fruit. Indeed, the cultivation of pawpaw is an ideal way to obtain fresh fruit with minimal effort. It is imperative to note that pawpaws have both a genetic and temporal self-incompatibility in regard to pollination, so at least two trees are required to yield fruit. Thus combined with their clonally-suckering/spreading growth habit, a generous amount of space is necessary for a successful harvest. 

For more information visit: http://www.pawpaw.kysu.edu/

Asimina triloba 2000-174-A on the Walk Across Kentucky

Tuesday, May 24, 2016

Solidago ptarmicoides (white goldenrod)

Solidago (goldenrod) is special genus for Kentucky.   Not only is it (generically) the state flower, but over 30 species grow in Kentucky; several of which are globally threatened or endangered, including Solidago albopilosa which grows nowhere else on earth.  For those who instantly cringe at the mention of ‘goldenrod’, it is worth dispelling the rumors that 1. They are a weedy group of plants (only a few attain such status), and 2. They cause allergies in the fall (completely false, goldenrod pollen is too heavy to be wind-dispersed).

The presumption that goldenrods are weedy has led many gardeners to shy away from their cultivation.  In fact, the majority of species make fantastic additions to both sunny and shady garden environments.  One such species is the ‘white goldenrod’, Solidago ptarmicoides.   It has only been reported in Kentucky a few times, and while it generally occurs in more northerly prairie communities, it is to be expected in dry open woodlands and barrens.  In Walk Across Kentucky Collections, it is thriving in a dry, sunny site amidst two bear oaks (Quercus ilicifolia) in the Cumberland Mountain Region.  

S. ptarmicoides (2014-202) in the Cumberland Mountain Region
As goldenrods go, Solidago ptarmicoides is quite uncharacteristic of the genus.  As the common name suggests, the inflorescences are predominately white as a result of the cream-colored ray flowers.  Leaves are small and linear, and the plants themselves grow much shorter than most goldenrods.  This species dissimilarity to most goldenrods has led many to accept it within a new genus, Oligoneuron.   In Oligoneuron, it becomes O. album because of its original name: Inula alba.  Because of a blatant paraphylly of Oligoneuron within Solidago, we have chosen to retain the name S. ptarmicoides.

Last season (2015) our mass planting of S. ptarmicoides remained in bloom from July until October, and was a huge hit for both staff and visitors.  The cream-white blossoms were prolific and dense, and our monocultured planting grew into a nice ground-cover.  This plant would be a great choice for areas with full sun, especially in dry rock-gardens.

Thursday, February 4, 2016

Podophyllum peltatum (mayapple)

There is an entire suite of native plants which are the first species to emerge as winter subsides, and which persist for only a short time.  These plants remain dormant for the majority of the growing season, emerging as harbingers of spring to maximize sunlight before the tree canopy has developed.  They are aptly named the ‘spring ephemerals’ and include some of the most stunning and well-known native wildflowers including trillium, Virginia bluebells, trout lily, and bloodroot.  Among their ranks is mayapple (Podophyllum peltatum), perhaps the most ubiquitous of all the ephemerals, yet whose flowers go largely unnoticed despite their considerable size.

Mayapple typically grows in colonies which spread belowground via rhizomes (underground stems that grow horizontally).  Borne along the rhizome are single stems which yield either 1 leaf, or bifurcate into 2 leaves.  The leaves are radially symmetric and after being pushed from the soil they open much like an umbrella. 
Mayapple leaves in various stages of emergence
Stems that bear two leaves produce a waxy white flower (1-2” across) from the axil where leaf bases are joined.  The flowers are thus hidden from above by the large leaves.  Likewise the mayapple fruits which resemble small lemons also tend to go unnoticed by humans, and are readily consumed by animals.  Turtles are regarded as primary dispersal vectors, though a variety of mammals may serve in this capacity as well. Mayapple fruit is considered by many people to be delicious, but be warned that all parts of the plant (including unripe fruit) are poisonous.
Waiting for a turtle?  A ripening fruit awaits dispersal

Podophyllum is a member of the barberry family (Berberidaceae), and until recently a genus that included a number of species of predominately Asian origin.  Currently, P. peltatum is the type species and sole member of Podophyllum after the Asian clades were reclassified into Sinopodophyllum, Dysosma, and Diphylleia.  Both the genus and specific epithet were named in reference to the distinctive mayapple leaf shape: “duck-foot-leaf” and “shield-shaped”, respectively.

Sinopodophyllum hexandrum (formerly Podophyllum hexandrum) is native to the Himalayan Region.  Leaves here are just emerging, and unlike Mayapple, flowers are pinkish and held above foliage.
Dysosma pleiantha (formerly Podophyllum pleianthum) is native throughout much of China.  Burgundy flowers hang below foliage as in Mayapple, but are borne in clusters (vs. solitary).

Diphylleia grayi (a close Podophyllum relative) is native to northern Japan.  Petals turn translucent when wet, leading to the common name 'skeleton flower'.

Should you consider cultivating mayapple, consider the natural ecology of this species.  Foremost, it is a colonizing plant that with spread over time.  This is not to serve as a warning against a potential garden bully (for it is not), but rather a suggestion of how stunning mayapple looks when grown en masse.  
Natural colony of maypple
Mayapple will reach 12-18” in height, and monocultures are equally as impressive as mixed plantings with other tall ephemerals such as Virginia bluebells or wild-hyacinth.  The ability of Podophyllum to tolerate a variety of sun and soil moisture conditions is remarkable.  Nevertheless, dappled shade in rich, moist soil is ideal. On the Walk Across Kentucky, mayapple colonies may be seen in the Appalachian Plateau, Arboretum Woods, Bluegrass, and Shawnee Hills Regions.
Podophyllum peltatum (2006-007) growing in the Bluegrass region of the Walk Across Kentucky.