Cactus family
This page is about cacti. The reader can find lots of species descriptions and cultivation instructions on the web and in books, so here it is mostly about some of my experiences from nature and the joy of making a few large-flowered species bloom.
The cactus family (Cactaceae) consists of succulent stem-assimilants, where the leaves, with few exceptions, are reduced to thorns that play no role in photosynthesis. There are 111-130 genera with at least 1650 species or perhaps closer to 1750 species. In addition, there is a large number of culturally produced forms and varieties. The genera belong to the American continent, with the exception of the genus Rhipsalis, which is native to East Africa, Madagascar, India and Ceylon. Several species have been introduced and more or less naturalized outside America. The flower is radially symmetrical and epigynous, as the florets and stamens are located above the ovary. The fruit is a berry. Several species have medicinal uses.
Rhipsalis species are epiphytes with meter-long plump hanging stems. It is
called the mistletoe cactus because the berries look like Viscum album and, like Viscum, they contain a sticky mucilage. The genus prefers rainforest, in contrast to the American genera, which primarily grow in dry environments.
The largest genus is Opuntia with approx. 300 species, and the genus is represented from Tierra del Fuego to the Yukon and is also found on the Galapagos Islands. Several species are extremely temperature tolerant. Thus, O. polyacantha photographed in Alberta, tolerates down to -46℃ in the Yukon and up to almost +40℃ in Mexico. Other species reach down to Tierra del Fuego, and some grow up to 4,600 m in the Andes.
The genus Pereskia belongs to the oldest and most primitive cacti, where the stems are only weakly succulent and still bear leaves, but the plants also have areoles with thorns. The flower is constructed as in the modern genera, albeit with fewer petals. Pereskia is native to South America. (photo courtesy of PixaBay).
Some cacti such as Epiphyllum have flat stems that resemble leaves, but they bear flowers and areoles with small hairs in notches on the edges corresponding to the knees of stems (nodia). Epiphyllum are epiphytes or lithophytes (see about Epiphytes), and the seeds must germinate on a suitable substrate before a plant can be established. They are most widespread in Central American forests and when cultivated they require more water during the growing season than most cacti. The stems form roots easily, and in the picture at right it happened after the stem tip touched the soil in a neighboring pot.
Growing cacti in most cases requires well-drained but nutrient-rich soil. You can use general garden soil or compost soil with a little gravel and pebbles added and possibly a little sphagnum. Phosphorous fertilizers promote flowering. Ideally, the soil should almost dry out between watering, and there should be virtually no watering during the rest period in winter. As many species tolerate full sun, it may be a good idea to put them outdoors in the summer.
Cacti are, with few exceptions (e.g. Rhipsalis), drought-adapted plants, so-called xerophytes. Their root system is usually close to the surface and widely distributed, so that it can absorb water from short-term showers, where the water only reaches a few cm into the ground. A number of anatomical and morphological characters reduce transpiration, and photosynthesis often follows the water-saving system CAM photosynthesis (see Xerophytes). At right: Apostoa lanata from Ecuador and Peru.
Cactus thorns are primarily a defense against herbivores. Length and number vary greatly from species to species, but
although they work against many animals, there are also quite a few animals that eat cacti. This applies especially to desert rodents and some birds. The fruits, which often have fewer thorns, are the preferred parts, and this may be appropriate as the animals promote the dispersal of the seeds. The fruits are also human food. Where cacti or camels are introduced, the camels are able to eat the thorny parts. The species above with yellow fruits is Opuntia echinocarpa, a cholla cactus from Joshua Tree National Park in California.
Above at left is a cholla cactus (Cylindropuntia bigelovii) that is dominant in several places in the Mojave desert, USA. At right it is a columnar cactus called Cardon (Pachycereus pringlei) from Baja California, and at left it is Echinocereus engelmannii from Joshua Tree National Park. It is also shown in the top photo of the page. There are more photos of cacti in the article in Danish: North American deserts.
The above three and the following two photos are from the Mendoza province in Argentina (Photos by Helene Heide-Jørgensen). If the reader can identify the first species above, a message via the contact form is welcome. The two other photos are of Denmoza rhodacantha.
Denmoza rhodacantha
Cfr. Pterocactus tuberosus
Maihuenia patagonica from Argentina is locally known as mother-in-law’s blanket. Car tires puncture if you drive over them.
The Huntington Botanical Garden in Los Angeles is a particularly impressive botanical garden with a large number of
cactus species in addition to plants from all over the world. At left: Cleistocactus sp.
Cactus bed at Huntington Botanical Garden.
Notocactus claviceps is visited in the right photo by a honey bee. It is a cushion or ball cactus from the Brazilian province of Rio Grande do Sol.
Echinocactus ingens, is a cushion cactus from the Puebla
limestone mountains in Mexico.
Lobivia caespitosa = Echinopsis maximiliana subs. caespitosa is from Bolivia and Peru.
Echinopsis pachanoi (syn. Trichocereus pachanoi) is a fast-growing columnar cactus that can branch from the lower part of the stem and become 3 m high. It is widespread in the Andes from Argentina to Peru, but is cultivated in many countries and can withstand frosts down to almost 10 degrees. However, it should not be left outside during the winter. It blooms near the tip of the shoot, and the flower only lasts well over a 24 hours. The flower is fully open at night, when in nature it is pollinated by bats. The stems contain a number of alkaloids, and in South America the plant is used in ritual ceremonies.
A series of eight photos with time information shows the opening of the Echinopsis pachanoi flower. It is approx. 25 cm long and a good 20 cm in diameter.
Cereus jamacaru (syn. Trichocereus jamacaru) is a 4-6 angular columnar cactus from NE Brazil. It is fast growing, can branch and become 6 m high. The narrowings on the left photo show the growth from year to year. The flowers can appear on almost the
entire length of the stem and are almost as large as those of Echinopsis pachanoi, but they are only open overnight. The plant does not tolerate frost. When it reaches the roof in the greenhouse, the top is cut off and planted in a pot after a few weeks of drying. The plant at left is 1.75 m tall and delivered 24 flowers in August 2019. Potted plants are placed in the garden in the summer to get as much sun as possible, which gives more flowers than in the
greenhouse.
Cereus jamacaru f. monstruosa (monstrosus) is a variety with numerous short irregularly placed ribs. It is stated in several places that it cannot flower, but here it has flowered several times from the upper part of the stem. It does not tolerate frost and does not use much water. Like the two previous species, it blooms at night.
Henning S. Heide-Jørgensen, October 2021.