Ozoroa
bhangazica: A newly described geoxyle
from Maputaland
by
Richard Boon and Braam van Wyk
The
woody genus Ozoroa is a member of the family Anacardiaceae. There are
approximately 45 species found from sub-Saharan Africa and the Arabian
Peninsula to South Africa. Twelve (now 13) species have been recorded from
South Africa. Recognising an Ozoroa is not hard because they have simple,
discolorous, opposite or whorled (occasionally alternate or sub-whorled)
leaves, parallel secondary veins that run to the leaf margin, and cloudy or
milky ‘latex’ (technically resin) when young parts are broken. It is the resin that gives
the South African species their common name, resintrees. Flowers are small, white
and arranged in panicles (‘sprays’). Immature fruits are green and when ripe, resemble
black raisins. Identifying plants to species level can be difficult because
there is a lot of infraspecific variation and there is little difference in the various species' flowers and fruits.
 |
| Most resintrees are shrubs or small trees like this Ozoroa obovata var. obovata Broadleaf or Coastal Resintree near St. Lucia. (R Boon) |
While most Ozoroa species are
shrubs or small trees, some are geoxylic suffrutices, also known as geoxyles,
geosuffs, geofrutices or ‘underground trees’. Geoxyles are woody plants that have
adopted a life form where most of the perennial woody parts are underground
and the aerial parts are limited and may be short-lived.
 |
| Diospyros galpinii Dwarf Hairy Star-apple is a common geoxyle on the Maputaland coastal plain. (R Boon) |
Geoxyles are especially common in
southern Africa, with particular concentrations in the high rainfall Afromontane
grasslands, the South African Highveld, and the high rainfall Kalahari Sands of
the Upper Zambezi Basin and surrounding Zambia and Angola. There is also an
especially high diversity and density of geoxyles in grassy environments of the
Maputaland coastal plain in north-eastern KwaZulu-Natal and southern Mozambique.
Maputaland Wooded Grassland is a vegetation type named for this feature. Superficially,
it looks like other grasslands but a closer look shows it supports a
remarkable abundance of geoxyles. The eminent British botanist Frank White, who
was an authority on African flora, introduced the term ‘underground trees’ and referred
to vegetation communities with a high presence of geoxyles as ‘underground
forests’. Once one recognises the geoxyles, it is not difficult to imagine Maputaland
Wooded Grassland as a subterranean forest. Some of the common geoxyle species found
growing in the vegetation type include Gymnosporia markwardii, Diospyros
galpinii, Eugenia albanensis, Parinari capensis subsp. incohata,
and forms of Ochna natalitia and Syzygium cordatum.
 |
| Maputaland Wooded Grassland at Ozabeni between Sodwana Bay and Lake Bhangazi North. There is a high cover of geoxyles and shrublets and a low cover of grasses and other graminoids. (R Boon) |
Also growing here, and more
specifically in the iSimangaliso Wetland Park, is another geoxyle recently
described as Ozoroa bhangazica. While newly described, the plant has
been known for many years and was included in the late Rob Scott-Shaw’s 1999 book
on rare plants of KwaZulu-Natal as Ozoroa sp. nov., the Maputaland Dwarf
Resintree. Prior to that, most botanists thought these plants were O. paniculosa
var. paniculosa, Resintree. The distribution map for O. paniculosa
in the field guide Trees of Eastern South Africa is incorrect as further
study has shown that the closest occurrence of this widespread, small tree is in
the Lubombo Mountains about 40 km inland of the KwaZulu-Natal coastline.
 |
| Ozoroa bhangazica Dwarf Maputaland Resintree growing in grassland unburnt for at least one season. These plants grow to a maximum of about 1 m tall and have relatively shorter and broader leaves than recently burnt plants. (R Boon1) |
In addition to the different growth
forms, there are several ways of separating O. paniculosa from O.
bhangazica. Ozoroa paniculosa has leaves arranged in whorls of three
or sub-whorled (vs alternate in O. bhangazica), relatively shorter and
broader leaves (vs usually long and narrow), the principal veins are raised and
prominent below (vs not raised and less conspicuous), the leaf margin
is undulate and thickened (vs only slightly thickened and not undulate) and
the upper surface of the leaf has short hairs or may become glabrous (vs always
essentially glabrous). The only other Ozoroa present on the Maputaland
coastal plain is O. obovata var. obovata, Broadleaf or Coastal Resintree.
It is easy to distinguish from O. bhangazica because it grows in coastal
bush or on the margins of bushclumps (vs in grassland), it is a shrub or small
tree (vs a geoxyle), and has broad, obovate leaves (vs usually long and narrow).
There is one other thing to keep in mind when identifying O. bhangazica—recently
burnt plants shoot vigorously from the woody rootstocks after fire and have
distinctly long and narrow leaves, while those that were not burnt during the
dry season lack vigour and have relatively short and broad leaves.
 |
| This Dwarf Maputaland Resintree is flowering well in spring following a winter burn. Note the relatively long and narrow leaves. (R Boon) |
There has been much debate as to
what drove the evolution of the geoxyle growth form that is found in many
unrelated plant families. Possible explanations include frost, herbivory, fire
in combination with high rainfall, and edaphic factors like nutrient-poor,
seasonally waterlogged soil. It is likely that all of these factors played a role, depending
on the region and specific locality. In Maputaland, there is no frost and
geoxyles are noticeably absent where soil becomes seasonally waterlogged. On
the other hand, plants that experience high rainfall and frequent fires, are not
browsed (at least in the case of O. bhangazica) and they lose vigour
when fire intervals are protracted, suggesting that at least in Maputaland, fire and high rainfall (and possibly nutrient-poor soils) are drivers.
Ozoroa bhangazica has a narrow range and is known only from two small areas
about 60 km apart at Lake Bhangazi North, which is south of Sodwana Bay, and on
the Eastern Shores north of St Lucia and to the south of Lake Bhangazi South.
It is possible that the species occurs in the intervening area because it is
hard to access and there appears to be suitable habitat. However, the area has
been explored by some botanists and it seems unlikely that they would have
missed recording this distinct species. We chose the name O. bhangazica
because both sub-populations occur near the Bhangazi Lakes. O. bhangazica
is therefore yet another endemic belonging to the Maputaland Centre of
Endemism.
 |
| Ozoroa bhangazica in gently undulating terrain south of Sodwana Bay. While elevation varies only slightly, geoxyles are not found in seasonally waterlogged depressions like the one partially visible in the middle distance on the right. Wooded grasslands in the iSimangaliso Wetland Park like this one are typically burnt annually or biennially. (R Boon) |
The Dwarf Maputaland Resintree is
a clonal plant with few to about 80 aerial stems emerging from an underground system
of woody axes. While the aerial stems superficially appear to be separate
plants, they are connected underground and genetically identical. Individual above-ground
stems are called ramets, from the Latin ramus (‘a branch’) and the
overall plant is called a genet, from the Greek genos (‘race, stock or
kind’), a reference to the identical genes. Clonal plants can be considered
individuals at the genet or ramet level.
 |
| The woody underground axis of this plant has been partially exposed by an animal digging. The two stems (and the other two partially obscured on the left) are genetically identically ramets. (R Boon) |
An interesting feature of clonal
plants is that they can be extremely long-lived and some have lost the ability
to reproduce sexually. An example of this comes from Tasmania, Australia where
a clone of the Critically Endangered Lomatia tasmanica King’s Lomatia
(Proteaceae) is known from a single population of about 500 genetically
identical stems covering an area of 1.2 km2. The plant is thought to be sterile as the
flowers never produce fruit and seeds. Using a count of tree rings, an individual stem has been estimated to
be 240 years old. Fossil evidence suggests that the
King’s Lomatia genet could be at least 43 600 years old, which would make
it one of the oldest living organisms on Earth.
 |
| Ripe Ozoroa fruits look like raisins. The discolorous leaves with parallel venation running to the margin are visible in this photograph of a Dwarf Maputaland Resintree. (R Boon) |
Dwarf Maputaland Resintrees flower freely and appear to produce viable seed and thus should be capable of sexual reproduction. However, establishment of new genets is probably rare because it requires bare ground with low competition from other plants, sufficient and sustained moisture and a gap between fires for seedlings to establish. The grasslands at the two localities burn annually or biennially and the current fire interval may not be long enough for young plants to survive. Fortunately, like other geoxyles, Ozoroa bhangazica is fire-adapted and as a clonal plant probably lives for a very long time and can continue to reproduce vegetatively between rare recruitment events.
We conducted a preliminary
conservation assessment using the IUCN methodology. While the overall
population is probably small and there are only two sub-populations, the plants
are protected in the iSimangaliso Wetland Park World Heritage Site and there is
no evidence that the population is currently threatened or declining. Our conclusion is
that Ozoroa bhangazica should be classified as Near Threatened until a
more detailed assessment of the two populations can be done.
References
The scientific description with a full list
of references can be obtained open source form here:
Boon, R.G.C. & van Wyk, A.E. (2025). A
new species of Ozoroa (Anacardiaceae: Anacardioideae) from
Maputaland, South Africa. Phytotaxa 714(2): 103–117. https://doi.org/10.11646/phytotaxa.714.2.1
Other references:
Eriksson, O. (1993). Dynamics of genets in
clonal plants. Trends in Ecology & Evolution, 8(9): 313–316.
Lynch, A.J.J., Barnes, R.W., Vaillancourt,
R.E., & Cambecèdes, J. (1998) Genetic evidence that Lomatia tasmanica
(Proteaceae) is an ancient clone. Australian Journal of Botany, 46(1):
25–33.
https://en.wikipedia.org/wiki/Clonal_colony accessed 17 September 2025
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