Aconitum
Aconitum, also known as aconite, monkshood, wolfsbane, leopard's bane, devil's helmet, or blue rocket, is a genus of over 250 species of flowering plants belonging to the family Ranunculaceae. These herbaceous, frequently toxic perennial plants are chiefly native to the mountainous parts of the Northern Hemisphere in North America, Europe, and Asia, growing in the moisture-retentive but well-draining soils of mountain meadows.
Most Aconitum species are extremely poisonous and must be handled very carefully. Several Aconitum hybrids, such as the Arendsii form of Aconitum carmichaelii, have won gardening awards—such as the Royal Horticultural Society's Award of Garden Merit.
Etymology
The name aconitum comes from the Greek word wikt:ἀκόνιτον, which may derive from the Greek akon for dart or javelin, the tips of which were poisoned with the substance, or from akonae, because of the rocky ground on which the plant was thought to grow. The Greek name lycoctonum, which translates literally to "wolf's bane", is thought to indicate the use of its juice to poison arrows or baits used to kill wolves. The English name monkshood refers to the cylindrical helmet, called the galea, distinguishing the flower.Description
The dark green leaves of Aconitum species lack stipules. They are palmate or deeply palmately lobed with five to seven segments. Each segment is trilobed with coarse sharp teeth. The leaves have a spiral arrangement. The lower leaves have long petioles.The tall, erect stem is crowned by racemes of large blue, purple, white, yellow, or pink zygomorphic flowers with numerous stamens. They are distinguishable by having one of the five petaloid sepals, called the galea, in the form of a cylindrical helmet, hence the English name monkshood. Two to 10 petals are present. The two upper petals are large and are placed under the hood of the calyx and are supported on long stalks. They have a hollow spur at their apex, containing the nectar. The other petals are small and scale-like or nonforming. The three to five carpels are partially fused at the base.
The fruit is an aggregate of follicles, a follicle being a dry, many-seeded structure.
Unlike with many species from genera in Ranunculaceae, there are no double-flowered forms.
Color range
A medium to dark semi-saturated blue-purple is the typical flower color for Aconitum species. Aconitum species tend to be variable enough in form and color in the wild to cause debate and confusion among experts when it comes to species classification boundaries. The overall color range of the genus is rather limited, although the palette has been extended a small amount with hybridization. In the wild, some Aconitum blue-purple shades can be very dark. In cultivation the shades do not reach this level of depth.Aside from blue-purple—white, very pale greenish-white, creamy white, and pale greenish-yellow are also somewhat common in nature. Wine red occurs in a hybrid of the climber Aconitum hemsleyanum. There is a pale semi-saturated pink produced by cultivation as well as bicolor hybrids. Purplish shades range from very dark blue-purple to a very pale lavender that is quite greyish. The latter occurs in the "Stainless Steel" hybrid.
Neutral blue, greenish-blue, and intense blues, available in some related Delphinium plants—particularly Delphinium grandiflorum—do not occur in this genus. Aconitum plants that have purplish-blue flowers are often inaccurately referred to as having blue flowers, even though the purple tone dominates. If there are species with true blue or greenish-blue flowers they are rare and do not occur in cultivation. Also unlike the genus Delphinium, there are no bright red nor intense pink Aconitum flowers, as none known are pollinated by hummingbirds. There are no orange-flowered varieties nor any that are green. Aconitum is typically more intense in color than Helleborus but less intense than Delphinium. There are no blackish flowers in Aconitum, unlike with Helleborus.
Monkshood produces light indigo-blue flowers, while Wolf's Bane produces whitish or straw-yellow flowers.
Horticultural trade morphology
The lack of double-flowered forms in the horticultural trade stands in contrast with the other genera of Ranunculaceae used regularly in gardens. This includes one major genus that is known solely by most gardeners for a double-flowered form of one species—Ranunculus asiaticus, known colloquially in the trade as "Ranunculus". The Ranunculus genus contains approximately 500 species. One other species of Ranunculus has seen minor use in gardens, the 'Flore Pleno' form of Ranunculus acris. Doubled forms of Consolida and Delphinium dominate the horticultural trade while single forms of Anemone, Aquilegia, Clematis, Helleborus, Pulsatilla—and the related Papaver—retain some popularity. No doubled forms of Aconitum are known.Ecology
Aconitum species have been recorded as food plant of the caterpillars of several moths. The yellow tiger moth Arctia flavia, and the purple-shaded gem Euchalcia variabilis are at home on A. vulparia. The engrailed Ectropis crepuscularia, yellow-tail Euproctis similis, mouse moth Amphipyra tragopoginis, pease blossom Periphanes delphinii, and Mniotype bathensis, have been observed feeding on A. napellus. The purple-lined sallow Pyrrhia exprimens, and Blepharita amica were found eating from A. septentrionale. The dot moth Melanchra persicariae occurs both on A. septentrionale and A. intermedium. The golden plusia Polychrysia moneta is hosted by A. vulparia, A. napellus, A. septentrionale, and A. intermedium. Other moths associated with Aconitum species include the wormwood pug Eupithecia absinthiata, satyr pug E. satyrata, Aterpia charpentierana, and A. corticana. It is also the primary food source for the Old World bumblebees Bombus consobrinus and Bombus gerstaeckeri.Aconitum flowers are pollinated by long-tongued bumblebees. Bumblebees have the strength to open the flowers and reach the single nectary at the top of the flower on its inside. Some short-tongued bees will bore holes into the tops of the flowers to steal nectar. However, alkaloids in the nectar function as a deterrent for species unsuited to pollination. The effect is greater in certain species, such as Aconitum napellus, than in others, such as Aconitum lycoctonum. Unlike the species with blue-purple flowers such as A. napellus, A. lycoctonum—which has off-white to pale yellow flowers, has been found to be a nectar source for butterflies. This is likely due to the nectary flowers of the latter being more easily reachable by the butterflies; however, the differing alkaloid character of the two plants may also play a significant role or be the primary influence.
Cultivation
The species typically utilized by gardeners fare well in well-drained evenly moist "humus-rich" garden soils like many in the related Helleborus and Delphinium genera, and can grow in the partial shade. Species not used in gardens tend to require more exacting conditions. Most Aconitum species prefer to have their roots cool and moist, with the majority of the leaves exposed to sun, like the related Clematis. Aconitum species can be propagated by divisions of the root or by seeds, with care taken to avoid leaving pieces of the root where livestock might be poisoned. All parts of these plants should be handled while wearing protective disposable gloves. Aconitum plants are typically much longer-lived than the closely related delphinium plants, putting less energy into floral reproduction. As a result, they are not described as being "heavy feeders" —unlike gardeners' delphiniums. As with most in the Ranunculaceae and Papaveraceae families, they dislike root disturbance. As with most in Ranunculaceae, seeds that are not planted soon after harvesting should be stored moist-packed in vermiculite to avoid dormancy and viability issues. The German seed company Jelitto offers "Gold Nugget" seeds that are advertised as utilizing a coating that enables the seed to germinate immediately, bypassing the double dormancy defect Aconitum—and many other species in Ranunculaceae genera—use as a reproductive strategy. By contrast, seeds that are not immediately planted or moist-packed are described as perhaps taking as long as two years to germinate, being prone to very erratic germination, and comparatively quick seed viability loss. These issues are typical for many species in Ranunculaceae, such as Pulsatilla.Award-winning hybrids
In the UK, the following have gained the Royal Horticultural Society's Award of Garden Merit:- A. × cammarum 'Bicolor'
- A. carmichaelii 'Arendsii'
- A. carmichaelii 'Kelmscott'
- A. 'Bressingham Spire'
- A. 'Spark's Variety'
- A. 'Stainless Steel'
Toxicology
Aconitine is a potent neurotoxin and cardiotoxin that causes persistent depolarization of neuronal sodium channels in tetrodotoxin-sensitive tissues. The influx of sodium through these channels and the delay in their repolarization increases their excitability and may lead to diarrhea, convulsions, ventricular arrhythmia, and death.
Marked symptoms may appear almost immediately, usually not later than one hour, and "with large doses death is almost instantaneous". Death usually occurs within two to six hours in fatal poisoning. The initial signs are gastrointestinal, including nausea, vomiting, and diarrhea. This is followed by a sensation of burning, tingling, and numbness in the mouth and face, and of burning in the abdomen. In severe poisonings, pronounced motor weakness occurs and cutaneous sensations of tingling and numbness spread to the limbs. Cardiovascular features include hypotension, sinus bradycardia, and ventricular arrhythmias. Other features may include sweating, dizziness, difficulty in breathing, headache, and confusion. The main causes of death are ventricular arrhythmias and asystole, or paralysis of the heart or respiratory center. The only post mortem signs are those of asphyxia.
Treatment of poisoning is mainly supportive. All patients require close monitoring of blood pressure and cardiac rhythm. Gastrointestinal decontamination with activated charcoal can be used if given within one hour of ingestion. The major physiological antidote is atropine, which is used to treat bradycardia. Other drugs used for ventricular arrhythmia include lidocaine, amiodarone, bretylium, flecainide, procainamide, and mexiletine. Cardiopulmonary bypass is used if symptoms are refractory to treatment with these drugs. Successful use of charcoal hemoperfusion has been claimed in patients with severe aconitine poisoning.
Mild toxicity as well as severe toxicity may be experienced from skin contact. Paraesthesia, including tingling and feelings of coldness in the face and extremities, is common in reports of toxicity.