#Cactaceae

• Ancistrocactus — A genus of succulent plants in the family Cactaceae, native to the arid and semi-desert regions of the southern United States (Texas) and northern Mexico. It comprises relatively small, globular to cylindrical cacti with well-defined ribs and areoles bearing strong central spines, at least one of which is long and sharply hooked, a morphological feature that gives the genus its name.
• Aporocactus — A genus of epiphytic or lithophytic plants in the family Cactaceae, native to the mountainous regions and forests of Mexico, characterized by long, slender, cylindrical, and creeping or pendulous stems covered with fine spines and large, tubular, brightly colored pink, red, or crimson flowers. In modern horticulture, the most famous species is Aporocactus flagelliformis (rat-tail cactus), widely cultivated in hanging baskets.
• Areola — A small circular area, pigmented or structurally differentiated, surrounding a central point, such as the darker ring of skin around the nipple or the space bounded by the secondary vein ramifications of a leaf. In botany, the term also denotes the microscopic structure or cushion of hairs or spines specific to cacti (Cactaceae family), from which flowers, new branches, or defensive needles develop.
• Ariocarpus — A genus of cacti endemic to the semi-desert zones of Mexico and southern Texas, characterized by extremely slow growth, flattened globular stems, and unique, triangular or rocky tubercles lacking classic spines at maturity; these succulent plants have a massive taproot used as a water reservoir and are highly prized by collectors for their large flowers and mimetic appearance mimicking surrounding limestones.
• Ariocarpus retusus — A cactus species endemic to the arid and semi-desert regions of Mexico (genus Ariocarpus), characterized by the absence of spines in adult specimens and the presence of robust, triangular, grayish-green tubercles, often retuse or rounded at the apex. Commonly known as 'living rock', this globose cactus is extremely slow-growing and features a massive taproot, being bio-structurally adapted to survive within the cracks of limestone rocks.
• Arrojadoa — A genus of xerophytic plants within the Cactaceae family, endemic to the semi-arid regions of eastern Brazil, particularly inside the caatinga vegetation. It is characterized by slender, cylindrical, erect or decumbent, jointed stems that develop a woolly and bristly apical cephalium from which bright, tubular flowers emerge, adapted for hummingbird pollination.
• Arrojadoa penicillata — A particular cactus species within the Arrojadoa genus, endemic to the state of Bahia in Brazil. It is distinguished by slender, highly branched, and often shrubby stems whose segmented tips form a dense apical cephalium covered with fine, long hairs resembling a small brush (penicillate), from which vivid pink or purplish-red tubular flowers erupt.
• Arrojadoa rhodantha — A xerophytic species of cactus within the Arrojadoa genus, endemic to eastern Brazil (particularly in the states of Piauí, Ceará, Pernambuco, and Bahia), characterized by cylindrical, semi-erect or scrambling stems that develop a ringed apical cephalium covered with brownish or white wool and stiff reddish bristles. Its flowers are tubular, intense pink-magenta or bright red, adapted for hummingbird pollination within rocky caatinga habitats.
• Arthrocereus — A genus of succulent plants in the Cactaceae family, endemic to the mountainous and arid regions of Brazil, particularly in the state of Minas Gerais. These species are structurally characterized by thin, cylindrical, poorly branched or decumbent stems, covered with dense and fine spines, producing large, nocturnal, white or pale-pink flowers adapted for pollination by moths.
• Arthrocereus microsphaericus — The scientific name of a rare and endangered cactus species belonging to the Arthrocereus genus, found exclusively in the mountainous regions of eastern Brazil. The plant is structurally recognized by its very small globular or cylindrical segments (hence the name 'microsphaericus'), with reduced spines, forming compact clumps at soil level and bearing major ecological importance in biodiversity conservation.
• Astrophytum — A genus of succulent plants within the Cactaceae family, native to the arid and semi-desert regions of Mexico and the southern United States (Texas). These cacti are characterized by globose or cylindrical stems, often lacking spines in adult state, decorated with prominent ribs and microscopic white dots formed by coarse hairs (trichomes), possessing a general star-like appearance reminiscent of a star or marine astroid.
• Astrophytum asterias — An endemic species of small succulent plants within the Astrophytum genus (Cactaceae family), with a globose, flattened stem completely lacking spines, typically divided into exactly 8 flat, regular ribs. Its greenish-grey surface is decorated with numerous trichomes (microscopic white dots made of tiny hairs), featuring large, woolly areoles in the center from which yellow flowers with a red-orange center emerge; it is a protected species, endangered in its native habitat of Mexico and Texas.
• Astrophytum capricorne — A species of xerophytic plants within the Astrophytum genus (Cactaceae family), native to the semi-desert regions of Mexico (Chihuahuan Desert), characterized by a spherical stem that becomes cylindrical at maturity, divided into 7-8 sharp ribs. The species is distinguished by its long, flexible, flattened, and twisted spines reminiscent of a goat's horns (or a capricorn's), and by its large, yellow flowers with a deep purple or red center.
• Astrophytum myriostigma — A species of succulent cacti within the Astrophytum genus (Cactaceae family), native to the mountainous and arid regions of central and northern Mexico. The plant has a globose stem completely lacking spines, typically divided into 5 prominent ribs, giving it a three-dimensional star shape; its entire epidermis is densely covered by thousands of trichomes (microscopic white dots), giving it a characteristic silver-white hue, and its large flowers are pure yellow without a red center.
• Astrophytum ornatum — The largest and most vigorous cactus species within the Astrophytum genus (Cactaceae family), endemic to the canyons and limestone slopes of central Mexico (Querétaro and Hidalgo states). The plant has a spherical stem in youth that becomes columnar at maturity, capable of reaching over one meter in height; it features 8 subtly spiraled ribs, is armed with long, rigid, yellowish spines, and its epidermis is decorated with ornamental curved bands of white trichomes, bearing large yellow flowers.
• Aylostera — A genus of perennial succulent plants in the Cactaceae (cactus) family, native to the high mountainous regions of Bolivia and Argentina, often structurally classified as a subgenus of Rebutia. These specimens are characterized by small globose stems arranged in dense clusters, featuring woolly areoles and spectacular, brightly colored infundibuliform flowers that arise delicately from the plant's base, being highly valued in horticulture for their increased structural resilience.
• Aylostera albiflora — A rare species of dwarf cactus native to the high mountainous regions of Bolivia, structurally characterized by minuscule globose stems forming dense clusters covered completely by fine, white, silky spines. Its specific name reflects the spectacular nature of its inflorescence, as the plant produces in spring delicate pearly white-pinkish flowers growing abundantly from the lower areoles, making it a highly sought-after piece in international succulent collections.
• Aylostera deminuta — A species of perennial dwarf cactus native to the arid rocky regions of Argentina and Bolivia, structurally recognized by its dark green cylindrical-globose stems covered with rigid brown or whitish spines. Its specific epithet emphasizes the reduced dimensions of the plant body, which compensates however with huge funnel-shaped, bright red or intense orange flowers arising delicately from the lower areoles, creating a striking visual contrast.
• Aylostera pseudodeminuta — A perennial species of dwarf cactus native to the mountainous and arid areas of Argentina, structurally classified as a close link within the Rebutia complex. The plant develops spherical or short cylindrical vibrant green stems covered with dense, brown or yellowish spines. Its specific name emphasizes the great morphological similarity to the deminuta species, from which it is delicately differentiated however by significantly larger funnel-shaped, brilliant bright red flowers that erupt abundantly from the lower areoles.
• Aylostera spegazziniana — A species of perennial dwarf cactus native to the mountainous provinces of Argentina, named in honor of the renowned botanist Carlos Luigi Spegazzini. The plant body is structurally formed of dark grey-green globose or short cylindrical stems, protected by short, pectinately arranged spines. It produces spectacular, deep red or scarlet funnel-shaped flowers that develop delicately from the side of the base, being recognized for its structural resistance to low temperatures during rest periods.