Support Species for a Dryland Food Forest, a Practical Example
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From its very inception, a natural system is involved in a continuous evolution, an ongoing succession of different stages toward increasing diversity and complexity, toward increasing stability, fertility and productivity until, eventually, the system reaches its climax – a final stage of relative stability where most of the energy is no longer used for growth but for maintenance and where the species composition remains relatively unchanged until a disturbance occurs, from a lightning that blows down a single tree to a catastrophic fire to human intervention.
When designing for a food forest, we are harmonizing with the succession that naturally occurs in nature, speeding up that process that leads to an increase in biomass and biological activity, an increase in the energy and nutrients that get harvested, stored and cycled and, eventually, an increase in the quantity and quality – structure and fertility – of the soil itself.
The great difference between a natural system and a designed human-managed system is that, in nature, only a tiny part of the global yields is directly available to us, since we are only a tiny part of the whole natural species assembly, while in a human-managed system almost every species is selected to provide us with some form of direct or indirect yield. We call “support species” those plants whose primary function is to support the growth of our main productive species, performing a key role in regulating the incoming energies of sun, wind and water, hydrating the soil and stabilizing the water cycle, harvesting nutrients from the air (i.e. nitrogen-fixation) and from different soil depths, creating new niches to welcome a diversity of living organisms both above and under the ground and, generally, putting the ecosystem back into function.
We can divide support species in three main groups, based on their expected lifespan and so on their different role in our planned succession of stages: we will have species that are short-term (4-5 years, exceptions up to 10), medium-term (10-20 years) and long-term (more than 20 years that will end up in the canopy) and, as in nature any element performs multiple functions, also each of these elements offers a plurality of yields. For the purpose of this list, only the species belonging to the canopy, understorey and shrub layer were taken into account.
A scale from 1 to 5 indicates a tree’s levels of use, namely the products of a tree in relation to the amount of resources – skills and/or tools – the processing of these products involves, 1 requiring the lowest and 5 the highest resource investment (adapted from Permaculture One, table 4.9.1, Italian edition).
- An intrinsic product, i.e. a function that the tree performs only by being there (e.g. N-fixing, windbreak, forage for honey bees)
- Human activity limited to the harvest of readily available products (e.g. picking fruit or collecting fodder for animals)
- Products that require simple processing – simple skills and/or basic tools (e.g. grinding Carob pods or collecting firewood)
- Products that require medium processing – medium skills and/or more advanced tools (e.g. working timber or preparing herbal remedies)
- Products that require high processing – high skills and/or advanced tools (e.g. fragrance extraction through distillation)
In addition to its levels of use, each tree is presented with: its centre of origin (N = native), the etymology of the name (E) and a general description (D). The oldest seedlings were planted 5 years ago, provided for free by the government and sourced by local nurseries, or spontaneously germinated on the site (e.g. Tamarisk) – all the species were already present in the bioregion.
Attention: The information provided, especially in case of food and medicines, is purely of an indicative nature and does not have to be put into use without an adequate knowledge and careful preparation.
Note on nitrogen fixation: when “N-fixing*” is marked with “*” the species is a non-nodulating legume, a species in the legume family that does not present the root-nodule symbiosis, as about
95% of the sub-family Caesalpinoideae which includes Carob, Poinciana, Senna, Honey locust, Jerusalem thorn, etc. (Pawlowski, Prokaryotic symbionts in plants). While some scientific sources state these trees do not fix nitrogen, recent research suggests that nitrogen-fixation occurs anyway. Indeed, some non-nodulating legumes have been found to produce as much or more nitrogen as many nodulating species, growing successfully in infertile soils and, in some cases, even dominating the site. Most likely, it exists a continuum from high to weak nodulating N-fixers, passing through the non-nodulating species that may fix some nitrogen, to end up with those ones that may fix none. A case-by-case analysis is therefore required. (Ashton and Montagnini, The silvicultural basis for agroforestry systems; Bryan, Leguminous trees with edible beans, with indications of a rhizobial symbiosis in non-nodulating legumes; Bryan et al., Toward a new concept of the evolution of symbiotic nitrogen fixation in the Leguminosae)
SHORT-TERM SPECIES – (after five years some of them, such as Sesbania sesban or Tephrosia spp, have exhausted their function and are not in place any more)
- Dodonaea viscosa
- Gleditsia triacanthos
- Senna bicapsularis (ex Cassia bicapsularis)
- Tecoma stans
Dodonaea viscosa subsp. angustifolia, Sapindaceae Sand Olive
E: Dodonaea after Rembert Dodoens (1516-1585), Flemish botanist. Viscosa from the Latin viscosus meaning “viscous” referring to the leaves that secrete a resinous substance. Angustifolia from the Latin angustus meaning “narrow” and folium “leaf”, literally “narrow-leaved”. Also the common name comes from the leaves, that can remember those of an olive tree.
D: Fast-growing 2-3m tall dense shrub (rarely up to 8m). Slender leaves with a very short petiole shining in the sun. Pollination of the unisexual flowers is by wind although bees have been observed collecting pollen too.
Gleditsia triacanthos, Fabaceae Honey Locust
Note: Although it can live up to 150 years, in this system is considered to be a short-term tree since, after the first very few years, the benefits of its nursing function are outweighed by the cons of its rampant thorns: at this stage, its role in the system has come to an end.
N: Central USA.
E: Gleditsia after Johan Gotlieb Gleditsh (1714-1786), director of the Berlin Botanical Gardens in the 18th century. Triacanthos comes from the Greek prefix tri- meaning “three” (from treis) and acanthos meaning “thorn”, literally “three thorns” or “three-parted thorns” as young thorns may appear before developing complex thorny structures. Locust is linked to the biblical story of John the Baptist who survived the wilderness by eating “locusts”, commonly suggested to be the pods of the carob tree, that to the 17th century religious immigrants to the USA somehow resembled the pods of Gleditsia triacanthos and Robinia pseudoacacia, that gained the fame of Locust tree. Finally, “honey” denotes the sweetness of the pod’s pulp.
D: 15-35m high multi-trunked tree. Solemn thorns perform a protective function against livestock damaging. Thornless (inermis) varieties do exist although their offspring may revert back to thorny exemplars. Male and female flowers are found on different trees but bisexual flowers are also present on each tree (polygamo-dioecious plant) and are pollinated by bees and other insects.
Senna bicapsularis (ex Cassia bicapsularis), Fabaceae. Christmas Bush, Winter Cassia, Butterfly Cassia
N: Widely introduced and naturalized, most likely native to Central America (in particular the Carribean basin) and Northern South America.
E: Senna from Arabic sanā, “bright light”, “radiant”, referring to its bright yellow flowers. Bicapsularis meaning “with two capsules” or “two rows of capsules” referring to the pods.
D: This rounded shrub reaches up to 5m in height, pinnate leaves and yellow flowers that appear in autumn and winter, resulting very attractive to bees, butterflies and birds. Being adapted to brushwoodlands, hedges and forest margins, riverbanks and riparian forests, it is an ideal short-term mulch-producing support species (it requires full to partial sun). Salt tolerant and moderately drought tolerant, the seeds are widely dispersed by wind and/or water.
Tecoma stans, Bignoniaceae Yellow Trumpetbush, Yellow Elder
N: Americas, from Southern USA to South America.
E: Tecoma from the Nahuatl (Aztec) word tecomaxochitl, meaning “trumpet-like flower”. Stans from the present participle of the Latin stare meaning “to stand” referring to its upright posture.
D: Shrub or small tree 5-8m tall. The sunshine yellow flowers occur in clusters at the end of the branches and are pollinated by bees and birds. The blooms appear in flushes throughout the growing season, followed by string-bean-like pods enclosing papery-winged seeds. Requiring full sun and temperatures that do not go below -3°C, it is widely diffused all throughout the tropics and subtropics, elected as the national flower of the Bahamas and Virgin Islands.
MEDIUM-TERM SPECIES –
- Acacia saligna
- Hibiscus tiliaceus
- Leucaena leucocephala
- Parkinsonia aculeata
- Prosopis spp
- Tamarix spp
- Vachellia farnesiana (ex Acacia farnesiana)
Acacia saligna, Fabaceae. Coojong, Western Australia Golden Wattle
N: Western Australia.
E: Acacia from the Greek akakia, the name given by the 1st century Greek botanist and physician Dioscorides, referring to the word akis “thorn” in allusion to the thorns of Acacia nilotica. Saligna “willow-like” (willow in Latin is salix) referring to the resemblance of the leaves, that are actually photosynthetic phyllodes: flattened petioles that look and function as leaves, typical of Australian acacias. Wattle, the common name to indicate an acacia of Australian origin, is also a matrix of interwoven wooden branches used in building and reinforced with a layer of clay or animal dung and straw. This so called “wattle and daub” technique was utilized by the early Australian settlers to build their huts, making use of acacia branches that came to be generally called Wattles.
D: Dense bushy shrub or small tree 3-9m tall, thornless with an abundant yellow flowering. Fast growing, drought resistant and tolerant of alkaline and saline soils.
Hibiscus tiliaceus, Malvaceae Sea Hibiscus, Beach Hibiscus
N: Tropical shores of the Pacific and Indian Ocean.
E: Hibiscus from the Greek hibiskos, name that the 1st century botanist and physician Dioscorides gave to Althea officinalis, another member of the Malvaceae family. Tiliaceus because of the leaf resemblance to the species of the Tilia genus. Its common names reflect its natural coastal habitat.
D: Small evergreen tree 4-10m high with a thick crown of widely-spreading branches. The brightyellow flowers with a deep-red centre open in the morning, deepen to orange as the sun gets higher
in the sky, and finally turn red before falling at the end of the day. Adapted to both littoral and terrestrial habitats, it commonly grows wild along coastlines, water courses, marshes and estuaries, so it is not a surprise it is particularly suited to moist and sandy soils. More remarkably, it has shown a high spirit of adaptation to arid saline areas, decreasing stem height and diameter, number of leaves and branches, leaf dry weight and both total and specific leaf area, while increasing proline leaf content (a common organic solute that plays an important role in the osmotic adjustments of the plants), all behaviours that show the ability to withstand water and salinity stress. (El-Juhany et al., Effects of water stress and salinity on the growth of Hibiscus tiliaceus trees)
Leucaena leucocephala, Fabaceae Leucaena
N: Southern Mexico and northern Central America (Belize, Guatemala).
E: Leucocephala from leukos in Greek meaning “white” and képhalos menaning “head”, describing its characteristic white spherical flowers. The genus name derives from the same root. The Oaxaca state in Mexico derives its name from the word uaxin that in Nahuatl (Aztec) means “the place where Leucaena grows”.
D: Present in three distinct forms: the common type is a small tree (variably shrubby and highly branched) up to 5m high, the Peru type is a medium-sized tree up to 10m while the Salvador type
gets up to 20m in height. Claimed to be one of the fastest growing trees in the tropics, it can withstand low to heavy rainfalls such as some salinity and waterlogging, although it performs better in well-drained soils. Deep rooted and frost intolerant, it often has flowers, immature and mature pods all present at the same time and, if enough moisture is present, flowering and fruiting occur all throughout the year. Flowers are self-fertile and mostly self-pollinated, although the frequent bee visits can lead to cross-pollination and the formation of interspecific hybrids.
Parkinsonia aculeata, Fabaceae Jerusalem Thorn
N: Sonoran and Chihuahuan deserts of Southwestern USA and Northern Mexico.
E: Parkinsonia after the English botanist John Parkinson (1567-1650) while aculeata refers to its thorny stem. The common name Jerusalem thorn does not refer to the historic city but, as for the Jerusalem artichoke, it comes from the distortion of the Italian word “girasole” (Spanish and Portuguese “girasol”) meaning “that turns toward the sun” maybe because already during the 17th
century it was noticed that the tree “in serene weather expands its leaves in the daytime and contracts them at night”. (Evelyn, Sylva, or a discourse of forest-trees and the propagation of timber in His Majesty’s dominions)
D: Small spiny tree 4-10m high naturally branching near the ground with a very open crown. Leaves are in strips (rachises) 20-30cm long with tiny leaflets that appear shortly after rain and fold up at night, dropping off within a few days and leaving the rachis to function as a leaf. Bright-yellow flowers are pollinated by bees and give birth to short light-brown pods. Its life span is not expected to be longer than 20 years.
Prosopis spp. (juliflora/pallida/chilensis), Fabaceae Mesquite
Note: There are many species of Prosopis with a distribution that ranges from -400m below sea level to 3700m above, with a variation in rainfall from 100 to 1400mm, although most species are found in semi-arid and arid regions all over the world. Being introduced in many countries, wrong identification and academic disagreement is a common situation. Moreover, hybridization between
Prosopis spp. is thought to be highly frequent and many documented species are likely hybrids. For example, triploid species have been observed from the hybridization between a tetraploid P. juliflora and a diploid P. pallida or P. chilensis (although P. pallida in Jordan is not much recurrent). Being more generic about the species of the tree is a way to avoid misleading information. (Pasiecznik et al., Identifying tropical Prosopis species: a field guide; Trenchard et al., A review of ploidy in the genus Prosopis, Leguminosae).
N: The ancestors of the genus may have originated in Africa, developing in two differentiated groups: Afro-Asian and American species. The spp. examined are part of this second group, being native to the deserts of the Southwestern United States, Mexico, Central and South America.
E: Prosopis is a Greek term meaning “burdock”, another spiny plant (maybe from prosopon, “face”). The common name, Mesquite, derives from Mizquitl, as the tree was called in the Nahuatl language spoken by the Aztecs. Juliflora from the Greek ioulos that means “down” but also “the first growth of the whiskers and beard”, denoting the downy facial hair of a young man that for extension it may have come to mean “catkin”, and flora, the Latin name for “flower”, denoting that flowers are grouped into long catkins.
D: Small- to medium-sized evergreen tree growing up to 10-12m tall, with an extensive lateral root system and a stout tap root that can penetrate as deep as 20m (as regards Prosopis juliflora, while other Prosopis spp. have been documented with a tap root up to 60m deep), although with a good surface water supply 90% of the roots can develop in the upper 100cm of soil. The elongated hermaphroditic flowers are pollinated mainly by wind and bees, while colonies of animals feed on the pods disseminating the seeds all over. P. juliflora has been shown to have species specific allelopathic effects, inhibiting the growth of some (but not all) species, and the leaf seems to contain more inhibitors than does bark and root, particularly discouraging the presence of grasses and plant diversity under its canopy. (Getachew, Allelopathic effects of the invasive Prosopis juliflora)
Tamarix spp., Tamaricaceae. Tamarisk, Salt Cedar
N: Eurasia and Africa.
E: The species name may derive from the Tamaris River (modern Tambre) in Spain. It may share the same etymological route as the river Thame, Tamesis in Latin, both deriving from the same proto- Celtic root tamo- meaning “dark”. In Galicia, where the river flows, roughly half of the non-Latin toponyms have been found to be Celtic, testifying the Celtic presence in the region from the 9th to the 1st century BC.
D: Species of shrubs or small trees with numerous slender branches and small scale-like leaves, usually growing about 1.5 to 6m high but that can reach the 18m. Insect pollination is required to set seeds that can germinate while floating in the water. The root system of the taller species can extend up to 50m laterally while the deep tap root can reach up to 30m beneath the surface, guaranteeing a high drought tolerance. Its fame though derives from its performances in highly saline and alkaline soils. Its salt-secreting leaves form an extreme niche that harbours different microbial communities depending on the geographical location of the plant. (Qvit-Raz et al., Biogeographical diversity of leaf-associated microbial communities from salt-secreting Tamarix trees of the Dead Sea region)
Vachellia farnesiana (ex Acacia farnesiana), Fabaceae Fragrant Acacia, Needle Bush
N: Mexico, Central America.
E: Vachellia after Rev. John Harvey Vachell (1798-1839), chaplain to the British East India Company in Macao from 1825-1836 and a plant collector in China. Vachellia species were considered members of the genus Acacia until the rectification of the genus in 2005. Farnesiana after Odoardo Farnese (1573-1626), an Italian nobleman that around 1550 maintained one of the first private European botanical gardens in Rome (the first botanical gardens of any time being started by Italian universities only a short time before, precisely the oldest one founded in Pisa in 1544). The species was imported to Italy under the stewardship of these Farnese Gardens.
D: 3-8m tall multi-trunked tree with tiny leaflets 3-5mm long. Light-demanding, drought-hardy and fire-retardant species that does not tolerate shade, it forms large thickets on disturbed sites (e.g. thorny woodlands or shrublands) or it can be well managed as a fast growing ornamental with a life span of 25-50 years. Its bright yellow-orange fragrant flowers are pollinated by bees and other insects and used to extract a distinctive perfume.
LONG-TERM SPECIES –
- Albizia lebbeck
- Allocasuarina torulosa
- Azadirachta indica
- Ceratonia siliqua
- Cupressus sempervirens
- Delonix regia (ex Poinciana regia)
- Tipuana tipu
Albizia lebbeck, Fabaceae. Lebbeck, Woman’s Tongue
N: Southern and Southeastern Asia, Northern Australia. The plant was though to be native also to North Africa, while it was actually introduced to Egypt from the East Indies before 1807 when
“hundreds of thousands were planted along roadways”. (Morton, Woman’s tongue, or Cha-Cha (Albizia lebbeck Benth.), a fast-growing weed tree in Florida, is prized for timber, fuel, and forage elsewhere)
E: Albizia after Filippo degli Albizzi, a Florentine nobleman that in 1749, coming back from Constantinople, introduced Albizia julibrissin to Italy and the European horticulture. Lebbeck form
the Arabic labakh, “Persian tree”. “Woman’s tongue” ironically refers to the pod’s rattling in the wind.
D: 15-20m (more rarely 30m) high medium- to large-sized tree with a dense shade-producing crown that can spread up to 30m in diameter. The tree growth is seasonal with a break at the beginning of
the dry season, when in it sheds its leaves during the hottest months of the year to sprout back with the first rains. Its hermaphroditic flowers made out of yellow-green filaments release a pleasant fragrance.
Allocasuarina torulosa, Casuarinaceae Forest Oak, Rose Sheoak
N: Australia, coastal areas of Queensland and New South Wales.
E: Allo- from the Greek allos, “other than”, “different to” Casuarina (Casuarina is another genus in the family, Allocasuarina is indeed the largest of the four Casuarinaceae genera and the only one to be completely endemic to Australia). “Casuarina” instead refers to the similarity between the leaves of the tree and the cassowary’s feathers (kasuari in Malay). Torulosa derives from the Latin torulos, “little protuberance”, referring to the wart-like occurrences on the cone segment. In the common name, the suffix –oak is due to the first Australian settlements in allusion to the characteristics of some species of the Casuarinaceae family, namely the habitat along river banks and the conspicuous medullary rays (channels of nutrient flow growing outward from the centre of the log similar to the spokes of a wheel), which reminded them of true oaks.
D: Slender tree 15 to 30m tall in favourable sites. What appear to be needle-like leaves are instead photosynthetic branchlets and the leaves, in whorls of four or five, are just visible to the naked eye when the needles are broken at a joint. Male and female flowers are on separate plants (dioecious plant) and pollination occurs mainly by wind, with birds feeding on the seeds and helping with their dispersion. It belongs to that group of non-legumes able to fix atmospheric nitrogen and it may live up to 40-50 years with occurrences over the 100 years.
Azadirachta indica, Meliaceae Neem Tree
Note: One of its main support function is that to give a natural pesticide, although a balanced heterogeneous ecosystem should not be affected by significant pest problems. As other trees in this list, it could have been dealt with as a main species.
N: Indian subcontinent and Southeast Asia.
E: From the Farsi azad “free” and derakht “tree” with the Latin indica meaning “of India”. The “free tree of India”.
D: Small to medium-sized tree usually up to 15m tall x 10m of crown (but can reach 30m x 20m). It normally bears fruit after 3-5 years becoming fully productive after 10 years. Pollinated by insects such as bees, but also moths and thrips, flowers are both bisexuals and male (andromonoecious plant). The species is predisposed towards cross-pollination but self-pollination may also occur. In India it is referred to as “village pharmacy” while in Swahili it is known as mwarubaini, meaning “forty” in allusion to the forty cures you can derive from it. It can live up to 200 years.
Ceratonia siliqua, Fabaceae Carob Tree
N: Horn of Africa and the Middle East.
E: Ceratonia derives from the Greek keration literally meaning “small horn” that came to indicate the pods of the Carob. In ancient times, precious metals and gemstones were measured against the seeds of the carob tree and the modern term “carat” (today 0.2g) reflects this tradition. The “solidus”, a pure-gold coin of the Roman Empire (used from 312AD until the 10th century), weighed 24 carob seeds, from which the wording “24-carat”, used to indicate pure gold. Siliqua, indicating the carob pods in Latin – probably alluding to their hardness – is also the name of another Roman coin (always around the 4th century AD) made out of silver and whose weight was 1/24 of a solidus.
It seems this important role was assigned to the seeds of the carob tree not because of their uniformity in weight, indeed they are not unusually invariant in seed mass (with a 23% variability against a 25% average) and this might actually reflect the conflict of interests between buyer and seller, one of whom would always prefer bigger seeds while the other would always look for smaller ones. Carob was probably chosen because of its ready availability throughout the Mediterranean and its useful size: one-carat diamonds were found in Roman antiquities and Yemeni beads dated to the 4th century BC. (Turnball et al., Seed size variability: from carob to carats)
D: 9 to 15m tall, semi-spherical crown and thick trunk. The green-tinted red elongated flowers are initially bisexual but usually one sex is suppressed during the development of functionally male and female mature flowers, to end up with male and female carob trees (dioecious plant) that is not common among legumes, with some hermaphroditic forms (evolutionarily speaking unisexuality is generally regarded as a derived character form a bisexual ancestral state). Pollination between male and female plants is mainly carried out by insects such as bees and flies, and secondarily by wind. Domesticated since 4000BC it has always played an important role in Mediterranean societies. The pods were probably the proverbial “locusts” eaten in the wilderness by John the Baptist. It can live up to 200 years.
Cupressus sempervirens, Cupressaceae Mediterranean cypress
N: Eastern Mediterranean.
E: Perhaps originally from the Akkadian (a Semitic language spoken in ancient Mesopotamia) kapàrru-isu “firm, stable tree” that became the Greek kypàrissos and the Latin cupressus.
Sempervirens in Latin means “evergreen”.
D: A slender 15-20m high tree, with a single sturdy trunk and scale-like leaves. Present in two forms: pyramidalis, with branches getting closer to the trunk in columnar and tapered shape, and horizontalis, less dense and with a more open crown. Male and female cones are on the same plant (monoecious plant) and, like all conifers, are pollinated by wind. Along with the Olive, one of the symbols of the Mediterranean flora and culture.
Delonix regia (ex Poinciana regia), Fabaceae Flame tree, Royal Poinciana, Flamboyant
E: Delonix from the Greek delos (evident, conspicuous) and onyx (claw), referring to the shape of the petals. Regia from the latin regis, meaning royal, regal, magnificent for its stateliness inspired by the tree’s shape, pods and blooming. Flamboyant, flame tree, the common name gives a perfect picture. Also known as Poinciana, from the genus in which the members of the current genus Delonix and some other plants now belonging to the genus Caesalpinia were formerly classified. Poinciana deriving from Phillippe de Longvilliers de Poincy, the French governor of Saint Christopher Island (West Indies) who is credited with introducing the plant to the Americas in the 17th century.
D: Regarded as one of the most beautiful tropical trees in the world, this 10-18m smoothly-barked tree has shallow roots and an umbrella-shaped crown of fern-like leaves which, with its nearly
horizontal branches, becomes wider than the tree’s height. Its brown pods can be as long as 60cm. The colourful flowers are very attractive to bees and birds that, depending on the geographical
location, carry out the pollination.
Tipuana tipu, Fabaceae Tipuana, Rosewood, Pride of Bolivia
N: Bolivia, Argentina and Brazil.
E: Genus and species’ names come from tipu, the South American vernacular name used to refer to the tree.
D: Large fast-growing tree that usually reaches 20m of height but can grow up to 40m. Adapted to a wide range of climatic conditions, evergreen in warm climates and deciduous when temperatures get colder. The bright-yellow hermaphroditic flowers produce one of the most peculiar legume pods, technically a samara (also called helicopter seed or whirlybird), a winged dry fruit constituted by a swollen end – where the seed is held inside – overhung by a thin wing. When the seed falls the wing generates a rotation causing a lifting movement, extending the free-fall time and increasing the opportunity of landing a long distance away from the parent plant where the seedling will not have to compete for light and nutrients. If the seed happens to fall in water, the wing will act as a floater. In Bolivia, Tipuana forms open forests, often in association with Schinopsis hankeana, Schinus molle, Jacaranda mimosifolia, Acacia visco, Tecoma garrocha and Dodonaea viscosa. (Cruz et al., Tipuana tipu (Benth.) Kuntze, Seed leaflet No. 55)
Main references (alphabetical order):
- actaplantarum.org/acta/etimologia.php (only verified sources)
- Nugent and Boniface, Permaculture plants: a selection
- Quattrocchi, Medicinal and poisonous plants
Plus over a hundred of different web pages, book extracts and papers (indicated only when detailed information is present).