Plants 101: Succulents

Plants 101: Succulents
The Sill seeks to educate and inspire all plant lovers. In our plant novice series, Plants 101, we introduce some of our favorite plant types, explore where they come from, and gently advise how to take care. 
What is a succulent?

They look great on a sunny sill or side table. They’re child-friendly since they’re spineless and generally safe in case you brush up against one. Plus, they’re real cute. All succulents are adapted to dry environments with full sun and no shelter. According to a NASA study, succulents have even been found to purify the air of harmful toxins. Succulents are excellent starter plants because they’re low maintenance.

Succulents (from the Latin word “succulentus,” for juice or sap) are defined by their moisture-storing capacity and come from many botanical families. Botanically-speaking, the term succulent refers to ANY plant that has evolved adaptations to survive hot arid environments. It is a term that does not refer to any specific family or clade of plants, and in fact many succulent plants are not related to one another at all.

The definition of succulents in the consumer world is semi-arbitrary, and may exclude many plants that have succulent traits, such as bromeliads and other tropical plants. It has been used by collectors and in the marketing world for so long that the term 'succulent' is simply an accepted colloquialism at this point. Often, one will find collections of ‘succulents’ marketed towards families with children, or as child-friendly options because many succulents are spineless and generally safe to bump into. Cacti, on the other hand, have been kept separate because of the potential danger from the spines, even though they are indeed succulents. 

Succulence can include many morphological characteristics: an epidermis with waxy cutin, thickened, fleshy leaves, an alternative mode of photosynthesis, and so on. Many plants would, by botanic definition, be considered succulent even though we do not normally think of them as such. For example, snake plants (Sansevieria) and Ponytail palms (Beaucarnea) have adaptations for surviving in desert conditions. Snake plants have thickened leaves and CAM photosynthesis, and Ponytail palms have a thickened, woody trunk for water storage. 

the sill succulents snake plants full

Cacti & Euphorbs

Like we said, all cacti are succulents, but not all succulents are cacti. Cacti are succulents from the family Cactaceae, which only are native to the New World/Western Hemisphere. Euphorbs are succulents from the plant family Euphorbiaceae, and are cosmopolitan in their distribution. The trait of succulence has evolved multiple times throughout plant history, each time as a response to climate shifts to more arid conditions. Euphorbia (Euphorbiaceae) has been evolving since the early Eocene (56-40MYA) to be adapted and speciate in arid environments, whereas Opuntia (Cactaceae), has only been evolving since the Oligocene (~39MYA). Other plants have evolved succulent characteristics, such as Yucca, Agave, and Aloe

WE ARE FAMILY  

Let’s take a look at the families that live under the succulent roof:  

The Stonecrop Family (Crassulaceae) 

The most commonly thought of and sought after family whenever one thinks of a succulent. Crassulaceae is a truly diverse family, called the stonecrop family. Plants in this family occasionally resemble stones, grow in between stones, and are resilient as...yep, stones. Unlike its namesake, no plant in this family is actually farmed as a crop, but rather propagated for the horticultural and ornamental trade. Most are best and easily propagated via fallen leaves and disheveled plants or cuttings. If you think about it, they are weeds in their native environments.

Common crassula include Crassula (Jade Plants), Echeveria (pictured below), Graptopetalum, Kalanchoe, Sedum, and Sempervivumone of the few succulents native to Europe and temperate Asia. In ancient Rome, it was grown the roofs of houses, not only to appease Jupiter—it was observed that thunderbolts would never strike these plants, so they were thought to ward off thunderbolts, sorcery and storm damage—but also to cool houses in the hot Mediterranean summers. We now know that it’s likely that the boulders this plant grows on are the real reason why these plants were rarely struck by lightning. 

the sill succulent plants echeveria full

The Stonecrop is an older family of eudicots (see eudicots: a larger grouping of flowering plants) that evolved about 60-100MYA. Their flowers are more primitive and undifferentiated than other eudicot plants. Their morphology is so diverse and pliable, it’s often hard to get a solid description on this family. In recent genetic studies too, Crassulaceae plant genetics are so pliable that it’s hard to do molecular work or even track the family’s evolution. What we can say is that Crassulean Acid Photosynthesis (CAM) was discovered first in this family and named after it. CAM photosynthesis is an alternative photosynthesis that evolved in hot, dry environments, so that the stomatal pores can be closed during the day. Its purpose is to help the plant better conserve water. It should be noted that this family is quite unique in that every member of this family uses CAM photosynthesis. CAM photosynthesis developed independently in other plant families as well, such as in Poaceae (the grasses) and Orchidaceae (the orchids). 

The Cactus Family (Cactaceae) 

All cacti are from the same family known as Cactaceae. The family gets its name from the Greek Kaktos (κάκτος), meaning ‘spiny plant’. Cactaceae is a New World family that has evolved relatively recently in the plant world, but has diversified quite a bit. This family has evolved to be completely succulent, with a trend of modifying their leaves to form spines. The branches are reduced to structures called areoles. One of the key identifying factors of cacti is the presence of areoles, as well as multiple spines coming from those areoles. Their flowers have many stamen, which produce lots of pollen, and they are often scented as well for their flying pollinators. Most cacti flower at night and usually for only one night. Night-blooming is an adaptation that helps to conserve water. Since the window for pollination is so short, cacti rely on their short-lived flowers to attract bats, insects and birds, all of find the flowers fragrant. The goal is to attract as many pollinators as quickly as possible. Most cacti reproduce easily by seed, but can also be propagated by segments or pads.

Pereskia is a genus of plants that is a sister to the cacti and is related to the ancestor of cacti. By studying Pereskia, we can get a better grasp of how cacti have evolved so quickly and how they modified their leaves so rapidly. It turns out that Pereskia is already semi-cactus-like in that they have leaves modified into spines, but also retain a few leaves. Only a few mutations are needed to turn all the leaves into spines. Many cacti have used their resources to evolve spines and water-conserving mechanisms, so they have not evolved too many secondary metabolites that are toxic. In other words, many cacti are edible, including species of Opuntia (Prickly Pear), Stenocereus (Dragonfruit), Hylocereus (Dragonfruit), Peyote,= Carnegiea (Seguaro). 

The Spurge Family (Euphorbiaceae) 

Euphorbiaceae is a family of flowering plants whose ancestor was tropical in origin. This is believed to be why out of most succulents, Euphorbs have the most toxic secondary metabolites—tropical plants defend themselves by synthesizing many poisonous compounds. All euphorbs, in fact, produce a latexy sap that is highly toxic to ingest and irritating to those who have a latex allergy. They have reduced flowers and are mostly wind-pollinated. Cultivated euphorb species include those within genus Euphorbia, Croton (pictured below), and Hevaea (true rubber tree). Most reproduce easily through pups or cuttings, although through seeds is also possible. 

the sill succulent plants croton gold dust full

They do not form associations with animals—other than perhaps shelter—and have retained their ancestral leaves, but the more desert-dwelling species are more often deciduous, with either reduced or somewhat waxy leaves. The leaves appear in the wet season or the springtime, and dropped during the dry season, and the euphorb takes on the appearance of a cactus. Remember, true cacti do not have leaves except for Pereskia. Euphorbs appear to have spines, but they are not true spines, rather, they are modified leaf stipules which are modified projections of petioles (leaf stalks). They do not have areolas, or obvious places where new growth will come from.

The Asparagaceae & Asphodelaceae Families (Asparagales)

Asparagoids have been, and continue to be, difficult to classify. In fact, most monocot plants have been difficult to classify as the characteristics to classify them have been vague and the morphology variable. Originally, most Asparagoids belonged to the lily family Liliaceae, as described by the French Botanist Jussieu, and loosely defined as plants with a perianth (petals & sepals) of six equal colored parts, six stamens, a superior ovary, single style, and trilocular capsule. Botanically, this is a vague description, and so Liliaceae became known as a group where basically all plants with six petals were placed. 

Over the years, families of plants were parsed out, some of them being Aloaceae, Agavaceae, Asphodelaceae, Dracaenaceae, and so on. These families were reclassified again and again, as botanists really didn’t know what to do with these plants. For a while these plants were classified based on geographic and evolutionary relationships. When DNA taxonomy became prominent in the 1990’s, the Angiosperm Phylogeny Group (APG), an international group of taxonomists, decided to overhaul the entire order and solidify Asparagales as an order with Asparagaceae and Asphodelaceae. This order of plants seems to have evolved about 110-125 MYA, and is actually one of the most rapidly diversifying groups besides Lamiales, with the highest rate of diversification.

The Asparagus Family (Asparagaceae) 

Asparagaceae includes succulent and semi-succulent plants such as Agave, Beaucarnea (Ponytail palms), Dracaena, Hyacynthus (Hyacinths), Sansevieria (Snake Plants), and Yucca. Many are propagated by divisions (Sansevieria, Agave, Hyacynthus) or cuttings (Dracaena). Asparagaceae gets its name from Asparagus, borrowed from the Ancient Greek Asparagos (ἀσπάραγος), borrowed from an earlier Persian word Asparag, which means “young shoot”. As the vegetable asparagus is indeed a young harvested shoot, this is appropriate naming.

the sill succulent plants snake plant full

The Asphodel Family (Asphodelaceae) 

Asphodelaceae includes the succulent and semi-succulent Aloe, Gasteria, Haworthia, and Hemerocallis (Daylilies). Most are propagated by divisions as these plants tend to produce many pups or suckers, or in the case of Hemerocallis, more bulbs. Asphodelaceae gets its name from the Greek, Asphodelus (ἀσφόδελος) which was the flower associated with the dead and the underworld. The greyish complexion and “lifeless” look of pallor green of these plants compared with other, more green plants made them the perfect fit for a flower of the dead. These plants were said to grow all along the fields of the dead, and the planes of the afterlife, according to Homer, the Greek writer, although it is said that the concept of Asphodels in the afterlife is more ancient.

the sill succulent plants haworthia full

BASIC INSTINCTS 

Here’s a brief summary on what succulents need and some pointers for keeping them healthy.

Sunlight 

Bright, full-sun to medium, filtered light. Full sun is ideal. (Learn more about light requirements here

Water 

Size matters. Water semi-weekly for smaller succulents or monthly for larger ones. Cacti require less water than do other succulents, like fleshy Echeveria or Aloe. Allow potting mix to completely dry out before watering. Water more frequently during warmer months as the soil dries out and in drier months, and fertilize weekly during growth. Do not overwater as overwatering will cause plant to rot. Better to underwater than to overwater. This plant may be a good starter for plant parents who water their plants too little. (Learn more about water requirements here

Humidity 

Succulents do not care. 

Temperature 

65°F-90°F (18°C-33°C). It’s best not to let it go below 60°F (15°C).

Size 

Dependent on species. Most grow slowly, so will remain the same size, or increase in size in flushes of growth. 

Common Problems 

Succulents are generally very easy-going plants. May get scale and mealybugs. Treat scale bugs and mealybugs as soon as they appear with weekly sprays of horticultural (Neem) oil.

Precautions 

Do not consume. Best practice is always to keep houseplants out of reach of small children and pets. (Learn more about plant toxicity here

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