Typically, an involucre with a clasping shape similar to a cup or urn subtends each of a thistle's flowerheads. The comparative amount of spininess varies dramatically by species. For example, Cirsium heterophyllum has minimal spininess while Cirsium spinosissimum is the opposite. Typically, species adapted to dry environments have greater spininess.
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The disc florets are bright yellow. One plant can produce many stems which mat together due to their spininess and form a small thicket. The fruit is an achene about half a centimeter long with many rigid pappus scales.
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Their rarity in cultivation is likely due to their extreme spininess and their particular tropical needs. The stems and sheaths are made into rope, baskets and binding in house construction, but, unlike many other rattans they are irregularly knobby and scarred, which generally excludes their use in worked and polished furniture.
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Not found above 1000 m, they are found in Thailand, Sumatra, Borneo, Java and the Malay peninsula. In all cases they form dense thickets, occupying hilly or low land rain forest or in the case of C. subangulatus, in Sarawak, heath forest. Their low quality and spininess limits cultivation and use.
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At about 1000 million years ago the organisms responsible for acritarchs started to increase in abundance, diversity, size, complexity of shape and especially size and number of spines. Their populations crashed during periods of extensive worldwide glaciations that covered the majority of the planet, but they proliferated in the Cambrian explosion and reached their highest diversity in the Paleozoic. The increased spininess 1000 million years ago possibly resulted from the need for defense against predators, especially predators large enough to swallow them or tear them apart. Other groups of small organisms from the Neoproterozoic era also show signs of anti-predator defenses.
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Flora of North America, Ribes roezlii Regel, Eduard August von 1879. Gartenflora 28(8): 226–227 description in Latin, commentary and figure captions in GermanRegel, Eduard August von 1879. Gartenflora 28(8): plate 982 color illustration of Ribes roezlii (red-flowered plant at left) The fruit is a red or purple berry up to 2.5 centimeters long which is covered in thick, long spines. Among other currants and gooseberries with overlapping ranges, such as mountain gooseberry (Ribes montigenum) or wax currant (Ribes cereum), the sierra gooseberry is especially notable for the large size and extreme spininess of its berries, and for the absence of a noticeable dried flower remnant at the end of the fruit.
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However, not all is mutually beneficial: the ants relish the sweet honeydew produced by scale insects which suck the sap of the acacia and therefore protect them as well, effectively providing entry to diseases. The development of myrmecophytism ("ant symbiosis") and spininess in African and New World acacia species was an adaptation to the presence of large faunas of effective browsing mammals. The ants' sting is very painful, causing a lasting burning and throbbing effect. The ants provide vital protection to the bull's-horn acacias day and night, and it has been shown(Janzen 1966, 1967, 1969) that without the ants, Acacia cornigera suffer greater damage from attacking insects and tend to be overgrown by competing plant species.
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Kali tragus has acquired a bad reputation for its spininess, its woodiness when mature, and its general ecological competitiveness, augmented by its tumbleweed nature, which enables it to spread rapidly over open ground. During the past century or more, the majority of the publications that dealt with the topic have discussed its pernicious nature, the increasing threats that the species poses, and how to combat its invasiveness; they largely have ignored its other attributes. However, even early publications did concede that the plant is of value as a forage in severely arid conditions where few other forage species are viable. As for its harmful competitiveness, most authors emphasised its invasiveness, though some did mention its value in regenerating overgrazed or otherwise abused land.
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