“Cacti are different.” This sentence holds true for many aspects of the functional morphology and anatomy of cacti in comparison to other perennial plants. The biomechanical adaptations, especially of tree-like columnar cacti, seem to be unique. The scope of this small review is to elucidate some of their specific load adaptation strategies and how they deviate from — or are similar to — typical hardwood trees.

Morphological and anatomical plant traits provide important characters for plant identification, and provide vital information to support classification systems based on molecular phylogenetic studies. The tribe Senecioneae (Asteraceae: Asteroideae) has recently been reclassified as a result of molecular phylogenetic investigations, and species with succulent leaves have been identified in several different clades of the tribe. We study the leaf morphology and anatomy of 20 selected species of Senecio s.l., embracing representatives of all distinct groups of leaf succulents in Senecioneae, and contrast the results with a molecular phylogeny derived from ITS sequence data. The leaves of the studied species vary as to their gross appearance (flat to terete, horizontally or seemingly vertically oriented, with or without ‘window’ areas) as well as with respect to their macro-anatomy (tissue succulence vs. all-cell succulence). The morphological and anatomical characterizations of identified groups correlate well with the clades found in the ITS-based molecular phylogenetic studies, and the reclassification of succulent-leaved species of Senecio s.l. into the segregate genera Caputia, Kleinia and Curio is strongly supported. Leaf characters provide easy-to-observe diagnostic characters to recognize the three genera.

Nomenclatural proliferation is defined and characterized as a phenomenon of explosive increase in the number of names within a taxon. The monophyletic genus Grusonia illustrates how the instability in the generic concept for this group of species has produced a disproportionate increase in names. This large increase in the number of names is due mainly to treatments presenting new combinations at the generic level without any significant reduction in the number of species through synonymy, and shows the uncoupling of the generation of new names from the publication of new species. Three historical nomenclatural phases in Grusonia are identified showing that the majority of the new names were proposed before any molecular phylogenetic reconstruction had an impact on the systematics of the group. However, molecular systematics has played an important role for the delimitation of a monophyletic genus. The lack of a solid phylogenetic hypothesis of relationships was one factor that promoted the superabundance of homotypic synonyms for these 17 species of North American grusonioids. In the face of this phenomenon, which we refer to as nomenclatural proliferation, the subgeneric categories in the subfamily Opuntioideae are historically devalued.

Morphological and functional characteristics of flowers have been the primary criterion for traditional plant taxonomy and systematic classification because of their assumed constancy among individuals within a population. The effects of resource competition and pollen limitation from those of inflorescence architecture were separately studied during flowering season of the species to investigate patterns of investment allocation and fruit set among flowers within inflorescences of Sedum praealtum. I found that architecture was primarily accountable for the variation observed in reproductive traits of flowers within inflorescences. Specifically, the S. praealtum inflorescences exhibit a proximal to distal investment allocation sequence from female-biased to male-biased flowers, whereas the observed differences in fruit set were at least partially attributable to pollen limitation in distal-positioned flowers. Given the opportunity for different contributions of female and male functions to reproductive success, potential gender specialization of flowers at different positions within the inflorescence are discussed.

Astroloba herrei Uitewaal (Asphodelaceae: Alooideae) is currently regarded as one of the rarest and most threatened species in the genus. The species is mostly recorded as having a small, restricted geographical distribution range, as well as a habitat that is vulnerable due, in part at least, to its proximity to human activity. Its distribution range is interpreted as disjunct, as the species is considered to be restricted to two widely separated areas: 1.) the immediate surrounds of Prince Albert in the Great Karoo, Western Cape Province, South Africa, and 2.) a contested spot north of Uniondale in the Little Karoo. We hypothesised that these two areas, separated by 100 km [60 miles], were contiguous, but not through the most frequented routes connecting these two spots. Map overlays for vegetation type, soil type, and geology were used to predict likely habitats in the more inaccessible region through which the areas could be connected, specifically along the northern (Great Karoo) slopes of the Swartberg. Based on the results, the most likely potential localities were identified and visited, and the species was found where predicted. Ground-truthing of the predicted range therefore confirmed that A. herrei is in fact far more widespread than previously believed. Its distribution stretches from west of Prince Albert, along the eastern Swartberg, and across the provincial border into the Eastern Cape Province, where it occurs along the R407 road that connects Prince Albert to Willowmore. At the eastern edge of its range it crosses the Swartberg to the south, and occurs north of Uniondale. Significantly, A. herrei has a natural range which in size by far outstrips that of a number of other Astroloba species. Based on the results of our work we propose that the conservation status of Astroloba herrei be changed from “Vulnerable D2” to “Least Concern”.

A new species of Gasteria from the Klein Karoo near Calitzdorp is named, differing from G. brachyphylla by its leaves which are spirally arranged and larger keeled, as well as its flowering which is during summer and autumn.

Bulbine dewetii (Asphodelaceae) is named; it is an obligatory geophytic cremnophyte from the sheer rock faces of the lower southern slopes of the Heks River Mountains (Western Cape, South Africa). Bulbine dewetii usually grows solitary (rarely proliferating and forming small groups) with soft pendent leaves, flowering during the month of November (late spring, S. Hemisphere), the flowers open during the afternoon and remain open during the night. The description of this taxon forms part of an extensive survey of cliff-dwelling succulent and bulbous-succulent taxa in South Africa and Namibia.

Taxonomically, Kalanchoe rotundifolia (Haw.) Haw. (Crassulaceae) is one of the most complex of the southern African representatives of the genus. The expression of its vegetative morphology, especially leaf shape and plant size, is exceedingly variable. The reproductive morphology is more constant in terms of the size and shape of the corolla tube and lobes, as well as in the upper part of the corolla tube and lower part of the corolla lobes invariably becoming twisted at the post-anthesis stage. However, flower colour ranges from a yellow-infused light orange through pinkish-red to scarlet. At present we conclude that treating the species as a variable complex in southern and eastern Africa, as well as Socotra, is taxonomically the most sensible. We provide an amplified description and geographical distribution map for K. rotundifolia, and discuss and illustrate some of the remarkably variable forms. A neotype is designated for the name Kalanchoe integerrima Lange.

Taxonomically, Kalanchoe paniculata Harv. has in the past been confused with K. brachyloba Welw. ex Britten. We clarify the application of the name K. paniculata, illustrate the species, amplify its description, and provide information on its taxonomic history, biology, uses, and distribution.

Recent field work in Gran Canaria (Canary Islands, Spain), mostly in March and April 2017, yielded first records of 10 species of Cactaceae, all originally introduced as ornamentals. Cylindropuntia bigelovii, C. imbricata, C. prolifera, Disocactus speciosus, Opuntia lindheimeri and O. microdasys are locally naturalized or likely to become so, whereas Ferocactus herrerae, Harrisia tetracantha, Lophocereus schottii and Trichocereus spachianus are considered casuals. All these species are illustrated, georeferenced localities provided and other useful information, especially with regard to their identification and invasion status (in Gran Canaria as well as elsewhere in the world) are also presented. The presence of two further species, Opuntia monacantha and O. robusta, both often considered doubtful in the Canary Islands, is confirmed from Gran Canaria. New data are also provided for Opuntia leucotricha and O. pilifera, two species that were recently recorded for the first time for Gran Canaria, that seem to have increased.

The names Agave gustaviana J.N.Haage & E.Schmidt and A. maximiliana Baker (Asparagaceae / Agavaceae) are typified in preparation of the conservation of A. maximiliana against A. gustaviana. For this purpose a specimen, “Agave maximiliana Hort. Kew Feb. 22^nd 1881 N.E. Brown s.n.” (K000543880) kept at K is designated as neotype. Since Baker (1877), when he published the name A. maximiliana, cited the earlier A. gustaviana as a synonym of the former, both A. gustaviana and A. maximiliana have the same type. The name A. gustaviana was published in 1874, i.e., three years before A. maximiliana, and will have to be adopted for this economically important species, unless the conservation proposal is successful.

Sequential flowering of sympatric plant species is a commonly observed phenomenon and is thought to contribute towards maintaining the pollinator community. Sequential flowering is also interpreted as a potential way to reduce competition for pollinators and to reduce interspecific pollen transport.

Within-season sequential flowering is well-known for many species assemblages and usually shows a staggering over weeks and months. Here, we report on the flowering behaviour of two unrelated sympatric cacti (both Cactaceae — Cactoideae) from N Argentina, Acanthocalycium thionanthum (Cereeae — Trichocereinae) and Parodia microsperma (Notocacteae). At the start of the flowering season, the two taxa exhibit a temporally stable sequential mass-flowering that is triggered by the first rainfall event after the dry season: On the 6th or 7th day after the rainfall, Parodia microsperma starts a 3-day “big-bang” flowering period, and on the 8th or 9th day after the rainfall, Acanthocalycium thionanthum also starts a 3-day “big-bang” flowering period, with 1 day of overlap with that of Parodia. The sequence and duration, including the 1-day overlap, has been found to be temporally stable in all study years, with c. 90% of all flowers buds of a population opening synchronously in years with average spring rainfall. Later in the season, after the fruits derived from these initial flowerings have ripened, opportunistic flowering (including sporadic local small-scale mass flowerings) is exhibited by both species with no apparent synchronization or sequence. Only once was a second “big bang” flowering observed, likely caused by above-average dry conditions. The species pair is notable for the massive “big-bang” flowering triggered by rainfall with a tightly staggered synchronization, as well as for the change in flowering strategy later in the season.

We describe a new species, Leipoldtia nevillei Klak, known from several populations between Soebatsfontein and Wallekraal in the coastal plain of Namaqualand, South Africa. The new species is easily recognized as a member of the Leipoldtia-clade by its smooth, xeromorphic leaves, mostly 10-locular fruits with large closing bodies and broad valve wings. In habit and floral morphology it resembles most closely the monotypic Hallianthus H.E.K.Hartmann, but it lacks the high turret-shaped fruits and the prominent subcentral elevations on the covering membranes that are characteristic for Hallianthus. In addition, L. nevillei differs from other species of Leipoldtia L.Bolus and from Hallianthus by its pale yellow or white flowers with a pale yellow centre. In the closely related Cephalophyllum the fruits form closing bulges below the covering membranes, whereas L. nevillei has closing rodlets below the covering membranes, as is typical for Leipoldtia.

Neoraimondia have short-shoots comprised of a large areole with indeterminate growth (‘Kurztriebcephalien’). Flowers of some other cacti are subtended by modestly large photosynthetic leaves. Many specimens of the organ pipe cactus, Stenocereus thurberi, seem to have all these traits: large short-shoots with indeterminate growth and fleshy photosynthetic leaves. Short-shoots in organ pipe cactus grow new photosynthetic leaves at their apical meristem and sometimes flower, branch, and form discrete areoles with new spines. However, unlike short-shoots in Neoraimondia, spherical short-shoots of Stenocereus thurberi seem to retain chlorenchyma and lack extensive cork development.