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ALL IN THE FAMILY

When Carolus Linnaeus created his binomial plant naming system--a hierarchical classification of all plants--in the 18th century, a plant received two Latin or Latinized names (genus and species) identifying it as a unique member of the world’s plant kingdom.  For instance, while many plants are commonly called daises, you know exactly what plant you have if you know it is a Gerbera jamesonii, Gerbera Daisy.  Now, a knowledge of plant families isn’t as helpful to the average gardener as a knowledge of botanical names, but it is fun to know as much about our favorite plants as we possibly can.
 
Each species is grouped into a genus by commonly held primary characteristics, and each genus grouped into plant families by more broadly similar characteristics.  An easy to follow analogy would be humans (genus homo, species sapiens sapiens) being placed in the family Hominidae, other members of which include gorillas and chimps.  You have to admit we are obviously more like chimpanzees (Pan troglodytes) than horses (Equus ferus caballus.)  (Incidentally, don’t Chimps live in trees, yet troglodyte means cave dweller?)

Monkey analogy aside (and yes, I know Chimps are not “monkeys”), these groupings do not necessarily make identifying their members an easy task.  A plant family, and even a plant genus, may hold a lot of variation in appearance.  This is because it is the similarities in reproductive parts (flowers, fruits and seeds), rather than more easily identified characteristics such as growth habit (tree, shrub, vine), annual or perennial, leafy versus spikey, and so forth, that determine the family ties.  Each plant family has a set of characteristics that differentiate it from other families.  The flower of the Peace lily (genus Spathiphyllum, family Araceae) is obviously different from that of the annual geranium (genus Pelargonium, family Geraniaceae), while it is very similar to other members of the araceae family like the Caladium (Caladium hortulanum) or Calla lily (Zantedeschia aethiopica.)
 
Sometimes the similarities are hard to spot without dissecting the flowers, examining cross sections of vascular bundles, or viewing pollen under a microscope.  Take the family Euphorbiaceae, which contains the genus Euphorbia, as well as genera Breynia, Acalypha, Codiaeum, Jatropha, Ricinus and moreA common characteristic among members of this plant family is that all flowers are small and unisexual (either a male flower or a female flower, not a flower with both sexual parts), although both male and female flowers can be found on the same plant.  Think of the small yellow flowers in the center of the colorful bracts of the poinsettia (Euphorbia pulcherrima.)  With no obvious similarity in flower, the Euphorbiaceae family also contains the Chenille plant (Acalypha hispida) with long dense pendant spikes of tiny bright red flowers resembling long fuzzy red worms.   Another member is the Croton (Codiaeum variegatum), a tropical shrub with colorful leathery leaves and small insignificant flowers, the male flowers having tiny white petals.  Even the notorious Caster-bean plant (Ricinus communis), who’s seeds produce a poison that you do not want to find in your mail box (get it?), is a family member.  This tall tree-like annual herb looks nothing like another family member, the popular houseplant Crown-of-thorns (Euphorbia milii), a succulent shrub whose stems are covered with sharp spines.

Just as with our own families, however, the closer the relationship, the more similar the primary characteristics.  I look a lot like my medium height, dark-haired, blue-eyed brother, and not so much like my tall, blonde, brown-eyed cousin.  In addition to small, unisex flowers, the genus Euphorbia shares a flower characteristic that is not shared by the rest of its family.  Euphorbia have a flower type known as a cyathium, a special way in which its flowers are grouped.  You can recognize the similarity in flower on the poinsettia to the flower on the large succulent Pencil cactus (Euphorbia tirucallii.)  The members of this genus still vary widely in broader characteristics.  Some are herbaceous annuals (Euphorbia graminea ‘Diamond Frost’) or perennials like the garden spurges, while others are leafy shrubs or trees (Euphorbia punicea—Jamaican poinsettia.)  A large number of euphorbias are succulents, some small and creeping (Euphorbia myrsinites), some tall and tree-like (Euphorbia trigona).  With over 2000 species in the genus, there are euphorbias in all shapes and sizes, all ultimately identified by their flowers.

Since the development of DNA sampling, many species are being reassigned and/or renamed as we gain a better picture of the genetic similarities and differences between plants.  Some of us would probably love to be reassigned to another family--richer, handsomer, more athletic, smarter, etc.  On the other hand, for most of us, family is where we are most comfortable, feel safer, and are accepted despite our less desirable characteristics!   
Posted: 2/25/2015 by Margot | with 1 comment(s)
Filed under: MargotGunn, TheGreatIndoors
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