Dichapetalum cymosum

Dichapetalum cymosum, commonly known as gifblaar from Afrikaans, or occasionally its English translation, poison leaf, is a small prostrate shrub occurring in the northern parts of Southern Africa. It is notable as a common cause of lethal cattle poisoning in this region and is considered one of the 'big 6' toxic plants of cattle in South Africa. A 1996 estimate of plant poisonings in South Africa attributes 8% of cattle mortality caused by poisonous plants to gifblaar. The majority (70%) of fatal cases are in Limpopo province, with 10% each in North West, Mpumalanga, and Gauteng. Fluoroacetate (the poison used to synthetically produce Compound 1080) occurs in all parts of the plant and is responsible for the toxic effects shown. Dichapetalum cymosum was first recognised as toxic by the early Voortrekkers entering the Transvaal, who were probably alerted to its lethality by natives living in the region. Above ground, the plant is seen as a clump of small, woody shrubs about 15 cm (6 in) high. Such a clump is typically a single plant, as gifblaar has a huge underground root system - likened to an underground tree - and sends numerous shoots above ground in favourable conditions. The most obvious above ground parts are the leaves - simple, alternate with initially fine hairs later becoming glabrous. The leaves are bright green in colour on both sides. The secondary veins form loops and do not reach the margin. The flowers are small and white, and occur as dense clumps in the early spring. Fruit formation is rare; the fruits are orange and leathery, are not poisonous and known to be consumed by the Bushmen. Identification of gifblaar in the field is important in prevention of toxicity and also in assigning gifblaar as the cause of toxicity in an outbreak. It is a small, low-growing, nondescript shrub and thus easily confused with other species. There are four principal 'confusers' in its habitat. These are Ochna pulchra (lekkerbreek) saplings, Parinari capensis (grysappel), Pygmaeothamnus spp. (goorappels) and the various gousiektebossies (various genera and species of the family Rubiaceae). The first three of these are non-toxic, but gousiektebossies are also toxic and another of the 'big 6' cattle poisons. Of the similar species, gousiektebossies and goorappel have opposite, not alternate, leaves. Goorappel leaves also have a characteristic bulge terminally, though only when mature. Grysappel and Ochna pulchra have alternate leaves, but grysappel has pale grey undersides to its leaves (its name means grey apple). O. pulchra leaves have secondary veins that are not looped and reach the margin, and the margin itself is dentate not smooth. Gifblaar occurs in dry, sandy areas in acidic soils, as well as the northern slopes of rocky hills in the southern parts of the African savannah biome. In South Africa, the distribution is within the so-called 'gifblaar triangle', the points of which are Mmabatho; Middelburg, Mpumalanga; and Musina. The traditional southern border of distribution is the Magaliesberg mountains. It also occurs in an isolated region in the far north of KwaZulu-Natal. Gifblaar is also found in Namibia, Zimbabwe, Botswana as well as southern Angola. Within its habitat certain indicator species are used to identify veld which potentially harbours gifblaar - this veld is called 'gifveld' by farmers of the region. These are the trees Burkea africana, Terminalia sericea, and Ochna pulchra, and also the shrub Parinari capensis. The latter two species can easily be mistaken for gifblaar. The toxic compound isolated as the cause of gifblaar poisoning is fluoroacetate, which was first isolated by Marais in 1944. The LD50 of this compound is 0.5 mg/kg which translates to about 200 g of dry plant material to kill a 500 kg cow. The compound itself is not toxic but undergoes lethal synthesis in the body while reacting with coenzyme A, yielding fluoroacetyl-Coenzyme A. This compound reacts with oxaloacetate to form fluorocitrate, which is toxic, being an alternate substrate for aconitase (normal substrate citrate). It binds to the aconitase but cannot be released, irreversibly binding the aconitase causing disruption to the Krebs cycle, leading to a severe inhibition of cellular respiration. Furthermore, fluorocitrate stops citrate from crossing from the cytoplasm into the mitochondrion, where it is needed. In the cytoplasm it becomes degraded. In cattle, death by acute cardiac arrest is seen following drinking or some kind of exertion. Affected animals will show dyspnoea and arrhythmias before this. There may occasionally be neurological signs such as trembling, twitching and convulsions. Death occurs 4 to 24 hours after ingestion. In rare cases, an animal will survive the initial period only to drop dead months later of heart failure - so-called chronic gifblaar poisoning. On post-mortem, leaves may be found in the rumen, cyanosis may be seen, as well as signs of heart failure - congestion, haemorrhage, and myocardial necrosis (on histopathology). Diagnosis is based on these as well as the presence of gifblaar in the camp, particularly if signs of consumption are seen. Tests can be done for monofluoroacetate in rumen fluid, kidneys and liver.