Arceuthobium
M. Bieb.
Herbs or shrubs, dioecious, semi parasitic on stems (sometimes endophytic), 0.5 - 7 cm
long, glabrous, variously coloured, tufted; branches dichotomous or verticillate, jointed, terete
or slightly angular, compressed. Leaves absent or reduced to minute opposite and connate
scales. Flowers axillary or terminal on branchlets, decussate or whorled; peduncle absent; pedicel short to nearly absent, coloured, 2 – 4 mm across, monochlamydous. Male flowers:
sessile, subglobose or ovoid in mature bud, with a central nectary; perianth lobes 3 or 4 (rarely
up to 7), free; stamens equal to perianth lobes; anthers sessile and adnate to each perianth lobe,
spreading, circular, unilocular, dehiscing by a slit. Female flowers: pedicellate, ovoid to ellipsoid
in mature bud, epigynous; perianth lobes 2, adnate to ovary, persistent; ovary inferior, ovate,
compressed; style single, short; stigma round or capitate; ovules not distinct. Fruits baccate,
ovoid, 1-seeded, mucilaginous and bi-coloured (distal and basal portions of different shades),
explosive at maturity; seeds without true integuments, usually 3 - 5 mm long, ovoid to lanceolate,
containing one (rarely 2) distal, cylindrical embryo, with copious endosperm.
North to Central America, West Indies, Mediterranean, NE tropical Africa, Sino-Himalayas to W. Malesia, ca 45 species; 2 species in India.
Host range. This genus is parasitic exclusively on conifers and not reported from any other plant species and thus exhibiting a very narrow host range for almost all the species. Some are restricted to a single host species. Secondary hosts are there when they are growing in association with a heavily infested primary host. Poor soil conditions and poor stem growth rate of the hosts are favourable to Arceuthobium.
Notes. The genus Arceuthobium holds the unique distinction of having representations in both the New and Old World. They occur in all the continents except Antarctica, Australia, South America and Africa.
This genus is economically important being a major parasite of the coniferous forests of the world, inducing “witches’ brooms,” which cause their hosts to suffer retarded growth and eventually die. In North American forestry, this is the most serious of all diseases. A substantial area of forests get infested leading to serious loss in timber volume and quality. There are some medicinal importance attributed to this genus.
North to Central America, West Indies, Mediterranean, NE tropical Africa, Sino-Himalayas to W. Malesia, ca 45 species; 2 species in India.
Host range. This genus is parasitic exclusively on conifers and not reported from any other plant species and thus exhibiting a very narrow host range for almost all the species. Some are restricted to a single host species. Secondary hosts are there when they are growing in association with a heavily infested primary host. Poor soil conditions and poor stem growth rate of the hosts are favourable to Arceuthobium.
Notes. The genus Arceuthobium holds the unique distinction of having representations in both the New and Old World. They occur in all the continents except Antarctica, Australia, South America and Africa.
This genus is economically important being a major parasite of the coniferous forests of the world, inducing “witches’ brooms,” which cause their hosts to suffer retarded growth and eventually die. In North American forestry, this is the most serious of all diseases. A substantial area of forests get infested leading to serious loss in timber volume and quality. There are some medicinal importance attributed to this genus.
KEY TO THE SPECIES
| 1a. Plants always visible for less than 3 mm long outside the host body, endophytically growing, appearing only as brown pustules on the surface of the host | 1. Arceuthobium minutissimum |
| b. Plants always visible for more than 5 mm long outside the host body and well branched | 2. Arceuthobium oxycedri |
