Hosta

Description

Hostas are herbaceous perennial plants, growing from rhizomes or stolons, with broad lanceolate or ovate leaves varying widely in size by species from 1–18 in (3–45 cm) long and 0.75–12 in (2–30 cm) broad. The smallest varieties are called miniatures. Variation among the numerous cultivars is even greater, with clumps ranging from less than four in (10 cm) across and three in (8 cm) high to more than six ft (200 cm) across and four ft (130 cm) high. Leaf color in wild species is typically green, although some species (e.g., H. sieboldiana) are known for a glaucous waxy leaf coating that gives a blue appearance to the leaf. Some species have a glaucous white coating covering the underside of the leaves. Natural mutations of native species are known with yellow-green ("gold") colored leaves or with leaf variegation (either white/cream or yellowish edges or centers). Variegated plants very often give rise to sports that are the result of the reshuffling of cell layers during bud formation, producing foliage with mixed pigment sections. In seedlings variegation is generally maternally derived by chloroplast transfer and is not a genetically inheritable trait.

The flowers are produced on erect scapes, generally taller than the leaf mound, that end in terminal racemes. The individual flowers are usually pendulous, 0.75–2 in (2–5 cm) long, with six petals, white, lavender, or violet in color and usually scentless. The only strongly fragrant species is Hosta plantaginea, which has white flowers up to four in (10 cm) long; it is also unusual in that the flowers open in the evening and close by morning. This species blooms in late summer and is sometimes known as "August Lily".

Taxonomy

Taxonomists differ on the number of Hosta species; there may be as many as 45. Accordingly, the list of species given here may be taken loosely. The genus may be broadly divided into three subgenera. Interspecific hybridization occurs since all the species have the same chromosome number (2n = 2x = 60); except H. ventricosa which is a natural tetraploid that sets seed through apomixis. Many cultivated hostas formerly described as species have been reduced to cultivars; these often have their names conserved, and retain Latin names which resemble species names (e.g., Hosta 'Fortunei').

as of October 2014

Cultivation

Hostas are widely cultivated, being particularly useful in the garden as shade-tolerant plants whose striking foliage provides a focal point. Though Hosta plantaginea originates in China, most of the species that provide the modern plants were introduced from Japan to Europe by Philipp Franz von Siebold in the mid-19th century. Newer species have been discovered on the Korean peninsula as well. Hybridization within and among species and cultivars has produced numerous cultivars, with over 3,000 registered and named varieties, and perhaps as many more that are not yet registered with the American Hosta Society. Cultivars with golden- or white-variegated leaves are especially prized. Popular cultivars include 'Francee' (green leaves with white edges), 'Gold Standard' (yellow leaves with green edges, discovered by Pauline Banyai) 'Undulata' (green leaves with white centers), 'June' (blue-green leaves with creamy centers), and 'Sum and Substance' (a huge plant with chartreuse-yellow leaves). Newer, fragrant cultivars such as 'Guacamole' are also popular.

The American Hosta Society and the British Hosta and Hemerocallis Society support Hosta Display Gardens, often within botanical gardens. Hostas are frequently exhibited at major shows such as the Chelsea Flower Show.

Cultivars

The following is a list of cultivars that have gained the Royal Horticultural Society's Award of Garden Merit.

Toxicity

While usually grown for ornamental purposes in the United States, all species of hosta are edible, and are commonly grown as vegetables in some Asian cultures.

However, hostas are toxic to dogs, cats, and horses due to the saponins contained in the plant. Symptoms include vomiting and diarrhea.

Pests and diseases

Hostas are eaten by deer, rabbits, voles, slugs and snails, which can cause extensive damage to collections in gardens. Some varieties seem more resistant to slug damage than others. Poisoned baits using either metaldehyde or the safer iron phosphate work well, but require repeated applications (and may be more toxic to other creatures despite claims to the contrary). Deer control tends to be variable, as anything other than fencing tends to work for a few years then ceases to work as they become accustomed to it.

Foliar nematodes, which leave streaks of dead tissue between veins, have become an increasing problem since changes in attitudes about pesticides since the mid-1990s in many countries have caused a resurgence in this once-controlled pest. There are no effective means for eliminating nematodes in the garden, although they can be controlled to the point where few or no symptoms are seen.

A potexvirus called 'Hosta Virus X' was first identified in Minnesota, USA in 1996. Plants that are infected must be destroyed as the disease can be transmitted from plant to plant by contaminated sap. Symptoms include dark green "ink bleed" marks in the veins of yellow-colored leaves, and/or tissue collapse between veins. It can take years for symptoms to show, so symptomless plants in infected batches should also be considered infected.