Helixanthera schizocalyx

Although it is only known from about 1,650 m above sea level on the summit area of Mt Mabu in northern Mozambique, Helixanthera schizocalyx perhaps also occurs at similar altitudes on nearby mountains that have not yet been investigated botanically.

Holotype specimen of Helixanthera schizocalyx collected from Mt Mabu by Tim Harris in 2008 (Image: RBG Kew)

Helixanthera schizocalyx is a hairless parasitic shrub, which grows up to 50 cm tall, attaching directly to the branches of small trees. The branches are somewhat flattened when young, becoming rounded and up to 4 mm in diameter when mature. The leaves are in (sub)opposite pairs. The blades are about 3–9 × 1.5–3.5 cm in size, thin in texture and oblong or elliptic in shape with a rounded or broadly-angled base and a tapering tip. The leaf stalks measure 4–12 mm long. The flowers are held in a spike 3.5–6.5 cm long at the end of the branches, with 35–50 flowers per spike, each on a short stalk. The bracts are inconspicuous, about 1 mm long, and are triangular with a small basal swelling. The small receptacle of the flower is minutely pimpled and the calyx is less than 1 mm long and lobed, usually to the base. The flower buds are rod-shaped, tapering towards the tip and slightly broadened and ‘shouldered’ towards the base, the four petals being yellowish-green. While mature flowers have not yet been observed, in other species of Helixanthera the petals fold backwards as the flower matures. The four stamens are attached to the petals and have short filaments about 1.5 mm long with two projections either side at the base. The slender anthers are locellate (divided into a series of chambers) and about 5 mm long. The style is about 7 mm long, and is 4-angular. The fruits have not yet been observed.

This new species is most closely related to Helixanthera verruculosa, a species thought to be confined to the Southern Highlands of Tanzania.

The genus Helixanthera is unusual in the Loranthaceae (tropical mistletoe) family in that the flowers of most species appear adapted to insect, rather than bird, pollination. Field observations are required to confirm this. 

Habitat of Helixanthera schizocalyx (Image: Tom Timberlake)

Because of its remoteness and distance from major population centres, the forests on Mt Mabu are not under any immediate threat. However, as development and road-building progress rapidly across the country after years of war, this habitat could come under pressure quite suddenly in the near future. The most likely threats would be clearance of the forest margins for agriculture, logging for selected species (although none of the trees there is particularly desirable) and wildfires that would slowly 'eat into' the forest margin in dry years. Mt Mabu is not yet formally protected, but discussions are underway to develop a conservation project there through Fauna and Flora International, Justica Ambiental (a Mozambican NGO), Madal (a private sector company that owns abandoned tea estates at the foot of the mountain), and the local government administration, with RBG Kew and its in-country partners, the Mozambique National Agricultural Research Institute (IIAM), having an advisory role.

Jonathan Timberlake and Hermenegildo Matimele on Mt Mabu (Image: Tom Timberlake)

Mt Mabu is one of a series of large granite-dome mountains ranging from southern Malawi to northern Mozambique. It supports the largest extent of medium-altitude (1,000–1,600 m) forest in southern Africa, yet had previously escaped the notice of biologists. It was first recognised from the study of Google Earth images (indeed, it is sometimes referred to as the ‘Google Forest’), and more detailed satellite imagery has estimated its extent at 7,000 ha.

In October 2008, Mabu was the focus of an expedition under a Kew-led Darwin Initiative-funded project looking at the biodiversity of these montane regions. This multinational expedition included participants from Kew's partners in Mozambique, Malawi and BirdLife International, as well as Kew itself, and confirmed that not only was the mountain indeed clothed in moist forest, but that this forest was intact and largely undisturbed. Numerous discoveries from across a range of biological groups were made during this and subsequent trips, including two new snake species, one new chameleon, seven new butterflies and a new freshwater crab. So far Helixanthera schizocalyx is the only new plant species to be confirmed, but others are likely to follow including a potentially new species of the citrus family (Rutaceae).

During 2009 these finds led to much UK and international media interest in the ‘lost forest of Mt Mabu’ and allowed Kew's partners in Mozambique to raise the profile, not just of Mt Mabu, but also of other montane areas in the country. It also highlighted the important role played by botanists and zoologists, herbaria and museums, in identifying such areas for conservation.

Habitat of Helixanthera schizocalyx (Image: Tom Timberlake)

There is a strong link between some species of Loranthaceae and birds, principally nectar-feeding sunbirds (Nectarina and Arachnothera) and white-eyes (Zosterops). The birds are attracted to the brightly-coloured, often red or orange, flowers that produce significant amounts of nectar, and in the process pollinate the plant, although this particular Helixanthera is believed to be insect - not bird - pollinated. Birds also play a vital role in seed dispersal. They are attracted to the coloured, gelatinous-sticky fruits of the mistletoe, the seeds of which are then wiped onto the branches of other trees. The seeds adhere and germinate, sending down root-like haustoria into the tree's cambium, from where the parasite obtains its nourishment.

A strong link also exists between loranths and a number of butterflies of the Lycaenid family (the blues), which are known to be very specific in their host requirements and to have a complex life-histories. The larvae of various sapphire butterflies (Iolaini group) tend to feed on different groups of loranths, illustrating the interdependence of forest species from host plant to parasite to butterflies and birds, and the need for integrated conservation planning. 

This species is known from only five recently-collected pressed and dried specimens, four of which are housed in the behind-the-scenes Herbarium at Kew (and the fifth of which has not yet been distributed to a scientific institution). The preserved specimens in Kew's Herbarium are made available to bona fide researchers from around the world by appointment.

Darwin Project in Mozambique

Kewbooks.com - Buy 'Mistletoes of Africa' by R. Polhill and Delbert Wiens

Kew Science News – Jan 2009: Google Earth helps Kew put ‘lost forest’ of Mount Mabu on the conservation map

The Observer – 21 Dec 2008: British team discovers lost Eden amid forgotten forest of Africa

The Telegraph – 21 Dec 2008: Scientists discover new forest with undiscovered species on Google Earth