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The bromeliads (Bromeliaceae)

By Petra

From the pineapple to the Spanish moss, from the florists 'bromelia' to the true wild beauties, these are the bromeliads.

The name 'bromeliads' is sometimes thought to come from the Greek word for rain and referring to to the rain gathering capability of many species, but actually the genus Bromelia and indeed the whole group is named after the Swedish medical doctor and botanist Olaf Bromelius (1639-1705).

HISTORY AND EVOLUTION

Bromeliads (Bromeliaceae) are a family of monocot flowering plants. There are around 3,170 species. Bromeliads are one of the basal families within the Poales and are unique because it is the only family within the order with septal nectaries and inferior ovaries. They are one of the more recent plant groups to have evolved. They originated in tropical South America in the tepuis of the Guyana Shield. Thomas Givnish and his team at the University of Wisconsin published a paper in 2007 in Aliso. They sequenced and analized the variation of ndhF gene, a rapidly evolving gene in the chloroplast DNA. In total DNA of 35 bromeliad and 16 closely related monocot species was investigated to infer relationships among present-day bromeliad genera. They calculated the extent of genetic divergence found among present-day bromeliads and calibrated it against the amount of such divergence among various other groups of monocots. Their findings when correlated with the geological history and history of life in the region reveal an interesting story of bromeliad evolution.

Bromeliads arose roughly 70 million years ago, as terrestrial plants with C3 photosynthesis, on moist infertile sites in the Guayana Shield. The most basal genus Brocchinia is endemic to the tepuis in the Guayana Shield and is placed as the sister group to the remaining genera in the family. To give a perspective: for the first 5 million years bromeliads coexisted with dinosaurs. At that time North and South America were separated, the Venezuelan highlands were lowlands ready to be pushed up, and the Amazon drained through Lake Maracaibo into the Pacific. Subsequently bromeliads spread centifugally in the New World. The greatest number of primitive species are native to the Andean highlands. But for one species the whole family is endemic to the Americas, with the geatest number of species in South America. The exception is the tropical west African Pitcairnia feliciana . It is thought to have reached Africa via long-distance dispersal approximately 12 million years ago. It is the only bromeliad species outside the Americas.

Picture: World distribution of bromeliads

Modern genera and subfamilies began to diverge from each other 19 million years ago, implying a great deal of evolution (and most likely, a lot of extinction) during the 51 million years of time since the ancestor of all bromeliads arose those 70 million years ago. Bromeliads appear to have begun invading drier areas in Central and South America beginning roughly 15 million years ago, at the same time as bromeliads underwent a major adaptive radiation involving the repeated evolution of epiphytism, CAM photosynthesis, impounding leaves, several features of leaf and trichome anatomy, and an accelerated rate at which new genera subsequently appeared. Givnish and his team call this the 'bromeliad revolution', it appears to have occurred just after the uplift of the northern Andes and the shift of the Amazon to its present course. They suggest that epiphytism may have accelerated speciation by increasing the ability of bromeliads to colonize along the length of the Andes, allowing bromeliads to occupy a cloud-forest landscape punctuated frequently by drier valleys. Insect-pollinated, relatively small flowers (like those in Brocchinia or Lindmania ) were ancestral for all bromeliads. Avian pollination (mainly by hummingbirds) appears to have arisen at least twice about 13 million years ago, at about the time hummingbirds themselves were diversifying. Members of three different lineages ( Hechtia , Puya and several genuses of Pitcairnioideae ) show several convergently evolved leaf and trichome traits, as is so often the case with adaptations for surviving drought.

The long-recognized subfamilies Tillandsioideae and Bromelioideae are monophyletic, respectively (each subfamily includes all descendents of a single ancestor). However Pitcairnioideae are strikingly paraphyletic, with both tillandsioids and bromelioids arising from within it. Given the ladder-like family tree recovered, Givnish and his team had to recognize eight subfamilies (instead of traditionally reckognized three), if each was to be monophyletic. As a result they described four new subfamilies, recircumscribed Pitcairnioideae and Navioideae , sunk Ayensua into Brocchinia and described a new genus Sequencia (named this was because it has been initially recognized based on its DNA sequence).

INTRODUCTION INTO BROMELIAD BIOLOGY

The family includes plants that look similar to each other but are ecologically very diverse, adapted to and widely represented in a number of climates. Approximately half the species are epiphytes, both mesophytic and xerophytic, with ecologically extreme aerophytes. The other half are litophytic and terrestrial species. Plants range from very tender moisture-loving to fairly cold-hardy desert species. They can be found at altitudes from sea level to 4200 meters, from rainforests to deserts. Bromeliads can be found in the Andean highlands, from northern Chile to Colombia, in the Sechura Desert of coastal Peru, in the cloud forests of Central and South America, in southern United States from southern Virginia to Florida to Texas, and in far southern Arizona.

Foliage take different shapes, from needle thin to broad and flat, symmetrical to irregular, spiky and soft – all depending on the ecological adaptations of the species at hand. Many desert dwelling species have really stiff, spiky, thin, long leaves that are as vicious to get entangled in as barbed wire. The foliage usually grows in a rosette, is the most widely patterned and colored of any plant in the world. Leaf colors range from maroon, through shades of green, to gold. Varieties may have leaves with red, yellow, white and cream variegations. Others may be spotted with purple, red, or cream, while others have different colors on the tops and bottoms of the leaves. Many of these color variations are artificially selected for by gardeners, but many are natural. Many of the terrestrial species are desert-dwelling, but are not succulents like for example cacti or agaves.

Many bromeliads (especially those from tropical rain forests) are able to store water in a structure formed by their tightly-overlapping leaf bases, these are the tank bromeliads. They utilise their water supply via special papillae (evolved from leaf pores) on the upper side of their leaf-bases. On the other hand the grey-leaved epiphytic Tillandsia species in cloud forests capture water only with trichomes, in the form of scales or hairs on their leaves. These trichomes also help to reflect sunlight in desert environments and insulate from frost ( Puya laxa ). Bromeliads use crassulacean acid metabolism (CAM) photosynthesis to create sugars. This adaptation allows bromeliads in hot or dry climates to open their stomates at night rather than during the day, which prevents them from losing water. A side effect of CAM type of photosynthesis is the slow growth exhibited by nearly all bromeliads. Usually CAM plants are typical of deserts, but intrestingly even rainforest bromeliads are CAM plants.

Root systems vary according to plant type. Epiphytic bromelads in general have only a poorly developed root system of auxiliary hard, wiry roots whoose main function is to attach the plant to the substrate (tree branches, rocks, even telephone wires). Terrestrial bromeliad species have complex root systems that gather water and nutrients.

The inflorescence produced by bromeliads are considerably more diverse than any other plant family. Some flower spikes may reach 10 meters tall while others only measure 2–3 mm across. Upright stalks may be branched or simple with spikes retaining their color from two weeks up to twelve months, depending on species. In some species the flower remains unseen, growing deep in the base of the plants. Some bromeliads are faintly scented while others are heavily perfumed.

Picture: The flower of Vriesea splendens. Each yellow flower blooms only for a day, but the red inflorescence keeps its colour for a few months.

The largest bromeliad is Puya raimondii , reaching 3–4 m tall with a flower spike 9–10 m tall, and the smallest is probably Spanish moss ( Tillandsia usneioides ). The spanish moss is also one of the strangest of the family as it grows relatively fast and with numerous drooping grey branches it really looks more like a moss than a bromeliad.

MINIATURE WORLD OF TANK BROMELIADS

Tank bromeliads actually represent miniature habitats, increasing the number of species found in an area. One study found 175,000 bromeliads/hectare (2.5 acres) in one forest. That many bromeliads can gather 50,000 liters (more than 13,000 gallons) of water. Thus a wide variety of organisms take advantage of the pools of water trapped by bromeliads. A study of 209 plants from the Ecuadorian lowlands identified 11,219 animals, representing more than 300 distinct species, many found only on bromeliads. Examples are species of ostracods, 2.5 cm(1 inch) long salamanders and tree frogs. Jamaican bromeliads are home to Metopaulias depressus , a reddish-brown crab 2 cm (0.75 inch) across, which has evolved social behavior to protect its young from predation by Diceratobasis macrogaster , a species of damselfly whose larvae live in bromeliads. Some bromeliads even form homes for other species of bromeliads. Bromeliad pools are also a nursery for many poison arrow frogs. The female frog deposits one egg per tank and then regularly visits each tadpole, laying an infertile egg to feed the tadpole. Many epiphytic species of Urticularia use the tanks as hunting grounds to catch mosquito larvae. And what do bromeliads get from these 'guests'? Well animals poo, and poo is a much better fertilizer than the usual soup of rotting plant bits are being cought in the tank. But some bromeliads went a step further – each year now more bromeliad species are confirmed to be carnivorous, trapping small animals, drowning and digesting them. Carnivorous species are for example Brocchinia and Catopsis . Brocchinia lives on the tepuis, tropical but cool, very wet and nutrient poor habitats, where many other carnivorous plants are found, most notably Heliamphora , of which all species are endemic to specific tepuis.

Picture: The tank of Vriesea splendens. In the center the stalk of the inflorescence and two pups are visible.

BROMELIADS AND PEOPLE

Humans have been using bromeliads for thousands of years. The Incas, Aztecs, Maya and others used them for food, protection, fiber and ceremony, just as they are still used today. European interest began when Spanish conquistadors returned with the pineapple (the fruit of Ananas comosus ), which became so popular as an exotic food that the image of the pineapple was adapted into European art and sculpture. In 1776 Guzmania lingulata was introduced to Europe, causing a sensation among gardeners unfamiliar to such a plant. In 1828 Aechmea fasciata was brought to Europe, followed by Vriesea splendens in 1840. These species were resilient enough that they are still among the most widely grown and accesible bromeliads.

In the 19th century, breeders in Belgium, France and the Netherlands started hybridizing plants for wholesale trade. Many exotic varieties were produced up until World War I, which halted breeding programs and led to the loss of some species. The plants experienced a resurgence of popularity after World War II. Since then, Dutch , Belgian and North American nurseries have largely expanded bromeliad production. These days with mass production and thus easily affordable prices, these beautiful plants are grown, sadly, for little more than a decoration that is to be discarded as soon as it starts to struggle for survival in tacky ceramic pots in a totaly unsuitable environment. I strongly support growing plants, but I find this sort of an attitude an insult to Nature.

PROPAGATING BROMELIADS

Bromeliads reproduce sexually by seed like any other plant, but they also reproduce vegetativelly in their unique ways. Very often the plant will only flower once and then slowly die away while growing new pups (a pup is a new vegetatively produced plantlet) spontanously at the base of the old plant. Desert species like Puya and Dyckia grow new pups spontanously at the base of the old plant, thus growing into a tight and inpenetrable clump. Growing in such close quarters is just fine for the plant, but if you wish to divide the clump – this can be done, but you have set yourself a real task. Expect to damage a lot of leaves and get your hands cut up as you won't be able to be precise enough with gloves. Use a good strong pair of pruning shears to divide the clump. The 'new' plant doesn't necessarily need to have roots as they will grow soon. Sprinkle damaged bits with charcoal powder, plant but do not water for a few days. Damaged parts of the plant may start to rot in moist soil and you can loose the whole plant. Plants like Billbergia flower once and then die, but not befor producing many pups at the base of the old plant. Eventually they grow into a circular clump – the centre emptying and the rims growing. They are xerophytic epiphytes and therefore pretty easy to divide. Species like Nidularium and Neoregellia are tricky as they produce only very few (often only one) pups at the base of the old plant. Just leave the pups to grow to a good size and, if you wish to replant, do so after the old plant has died away. Some Neoregellia -s also grow pups on short stalks even before they flower. These are the easiest and least messy to divide: cut the stalk and plant the pup to a depth of approx 1 cm, leaving the stalk in place. Thats it, just wait for the roots to grow and water regularly. In the wild these stalked pups would root wherever they would touch the substrate – kinda like strawberries. Maybe one of the weirdest is the pineapple that can be grown from the tuft of leaves on top of the pineapple fruit. I dedicated one whole article to this.

Just a few words on growing bromeliads from seed: many of the epiphytes have tiny seed with feathery plumes that enable it to be carried by wind and to adhere to surfaces. This seed is short lived, only viable for a few days or weeks. For an epiphyte this makes sence as much more seed can be produced and the plant can only grow in a specific environment anyway. The terrestrial species have larger, hardier seed that is viable for a longer period. You can pollinate your plant's flowers using a delicate brush – each flower lives for a day or two. The seed takes sometimes up to 9 months to mature. Most bromeliads are surprisingly easy to grow from seed and grow quickly when young. Sow terrestrial species just as you would sow vegetable seed and sow epiphytes like carnivorous plants – on sifted wet peat on surface. Keep moist, they germinate in a few days.

GENUSES

The old view of taxonomy within Bromeliaceae separates the family into three subfamilies: Bromelioideae , Pitcairnioideae and Tillandsioideae . But the latest reasearch has shown that there are actually eight subfamilies:

1. Brocchinioideae:
Brocchinia (20 species)

2. Tillandsioideae:
Alcantarea (23 species)
Catopsis (18 species)
Glomeropitcairnia (2 species)
Guzmania (207 species)
Mezobromelia (9 species)
Racinaea (61 species)
Tillandsia (609 species)
Vriesea (261 species)
Werauhia (87 species)

3. Pitcairnioideae:
Deuterocohnia (incl. Abromeitiella) (18 species)
Dyckia (130 species)
Encholirium (22 species)
Fosterella (30 species)
Pitcairnia (331 species, incl. Pepinia (57 species) )

4. Bromelioideae:
Acanthostachys (2 species)
Aechmea (255 species)
Ananas (7 species)
Androlepis (1 species)
Araeococcus (9 species)
Billbergia (64 species)
Bromelia (56 species)
Canistropsis (11 species)
Canistrum (13 species)
Cryptanthus (66 species)
Deinacanthon (1 species)
Disteganthus (2 species)
Edmundoa (3 species)
Eduandrea (1 species)
Fascicularia (1 species)
Fernseea (2 species)
Greigia (33 species)
Hohenbergia (56 species)
Hohenbergiopsis (1 species)
Lymania (9 species)
Neoglaziovia (3 species)
Neoregelia (112 species)
Nidularium (45 species)
Ochagavia (4 species)
Orthophytum (53 species)
Portea (9 species)
Pseudaechmea (1 species)
Pseudananas (1 species)
Quesnelia (20 species)
Ronnbergia (14 species)
Ursulaea (2 species)
Wittrockia (6 species)