Bromeliaceae an introduction

[Derrick]

Bromeliad Ant-Plants: An Introduction.

Most bromeliads are unique due to highly specialised adaptations that enable the storing of phytotelmata (aquaria-like water reserves) and/or they have trichome coated leaves that enable highly efficient intake of water and nutrients.  Indeed, these are sometimes derived entirely from atmospheric sources. I add the cautionary word sometimes because many so-called 'airplants' derive some water and nutrients from organic derived leachates percolating down forest supports during rain or even heavy fog events.  Yet, some airplant species are able to grow quite capably on inorganic supports such as tiled roofs or even electricity cables.  Phytotelm (tank) bromeliads trap organics and atmospheric dusts in the centre of their leaf rosettes and/or leaf axils, thus enabling access to through-fall nutrients.

  As we will see, both phytotelm and tankless bromeliad types often provide homes to resident life forms both macro (usually arthropods or amphibians) and micro species (algae, cyanobacteria etc.,) and all help to supply plant nutrients.

Bromeliad Taxonomic Changes.

It has long been accepted that the Bromeliaceae had only three sub families, Pitcairnioideae with winged seeds, Tillandsioideae with plumose (feathery) seed and Bromelioideae having fleshy, fauna dispersed fruits.

  Now due to the results of DNA studies there is a new phylogeny for Bromeliaceae that creates an additional five sub-families.  The resulting eight subfamilies are here listed in the order they are believed to diverge from their ancestral forms.  (Givnesh et al. 2007.)

Brocchinioideae are endemic to the ancestral Guyana Shield; type Brocchinia.

Lindmanioideae are also endemic to the ancestral Guyana Shield; type Lindmania.

Tillandsioideae are mostly air plants; sample genera Tillandsia, Vriesea.

Hechtioideae have mostly xerophytic forms; type Hechtia.

Navioideae are also endemic to the Guyana Shield but with one species found on the Brazilian Shield, sample genera, Brewcaria, Cottendorfia, Navia, Sequencia, and Steyerbromelia.

Pitcairnioideae; sample genera, Abromeitiella, Deuterocohnia, Dyckia, Encholirium, Fosterella and Pitcairnia.

Puyoideae is a sister clade to Bromelioideae, type genus Puya.

Bromelioideae is a sister clade to Puyoideae; sample genera, Aechmea, Ananas, Cryptanthus, Bromelia and many others.

  It will probably take decades for this upheaval in the world of bromeliads to work its way into popular literature. However, having any clade (branch) of an evolutionary tree divulging at an earlier time does not necessarily mean its members are any more primitive than later divulging clades.  Early phyletic branching does not mean that evolution has stopped, as we will see so definitely in Brocchinia.

 

Bromeliad Eco-physiological Types.

Professor David Benzing (2000) distinguishes five eco-physiological bromeliad forms, however because this was published prior to the above revision he only used the older sub family divisions.

 

1. Terrestrial herbs of subfamily Pitcairnioideae and many Bromelioideae that use roots to acquire water and nutrients due to their leaf trichomes being non-absorbent.

2. Terrestrial Bromelioideae with leaf bases that form rudimentary tanks into which some axillary roots may penetrate.

3. Terrestrial or epiphytic herbs in sub-family Bromelioideae with roots that are of little importance concerning water and nutrient intake.  Leaf bases form extensive phytotelmata along with an obligate CAM pathway and possession of at least semi-absorbent trichomes.

4. Tank forming, mostly C3 epiphytes in subfamily Tillandsioideae and some Brocchinia (now in Brocchinioideae) with many highly efficient water and nutrient gathering trichomes on their leaf bases.  Roots primarily acting only as hold fasts.

5. Tank less epiphytic or lithophytic, succulent/xerophytic Tillandsioideae with absorbent trichomes covering entire leaf areas.  Roots, if any are hold fast only.  Most ant mutualists fit here.

[Derrick]

Bromeliaceae Sub-family Tillandsioideae,

Tillandsia Carl von Linnaeus published in Species Plantarum 1, 1753.  This genus has been somewhat of a dumping ground for taxonomically difficult to place species; hence, DNA and other modern research methods will probably change the names within this genus substantially.  They are named after Elias Tillands a Finnish botanist who died in 1693.

  There are about 551 species (Smith & Till 1998 cited by Chew et al. 2010.) occurring from as far south as central Argentina & Chile (Till 1992 cited by Chew et al. 2010) northwards throughout South and Central America to Mexico and into climate-suitable regions of southern USA, especially Florida.

Their enormously widespread and varied habitats range from deserts to hot humid forests to winter-cold mountains and their forms, leaf textures and sizes vary immensely from miniatures of only a few cm. to plants some 5 metres (16.5 ft.) tall.

  Atmospheric or Airplant Tillandsia, the form that most concern us herein, have leaves that are at the very least xerophytic, often extremely so and are sometimes succulent; furthermore, they often show “high tolerances for severe tissue desiccation.” (Benzing & Dahle 1971 cited by Benzing & Renfrow 1971.)  Hence, some species have physiological traits reminiscent of resurrection plants.

  In contrast to phytotelm (tank) bromeliads, which all have negative geotropism (shoots always grow away from the earth), most non-tank forms are ageotropic meaning their shoots are not affected by gravity; hence such plants will grow in whatever direction their buds first appear.  This may be horizontal especially on perpendicular cliffs or tree trunks or even hanging from the lower sides of variously inclined branches.  As we have seen, this is a characteristic common to many epiphytic myrmecophytes especially ant-house species.

  Air-plant Tillandsia roots are usually tiny, acting primarily as holdfasts and most water and nutrient absorptions are facilitated by extremely efficient trichomes that often densely cover their leaves giving plants at least a whitish-grey colouration.  However, those species most adapted to intense insolation and its consequent spells of aridity become an ever more photon-reflective white. It follows that plants with particularly white leaves tend to originate from more sun exposed and/or more arid habitats where stringent requirements to maintain water budgets overrides the imperative to photosynthesize.  Yet as we will see, some ant-plant Tillandsia species (or some regional forms of more widespread species) often predispose to greener leaf colours; therefore, they are not always among the more aridity adapted of their genus.  Certainly, as already hinted, the degree of tolerances to aridity and/or high insolation levels is often dependent upon the original provenance of wide ranging species.  Nevertheless, for Tillandsia species in general “maximum rates of photosynthesis are quite low while light demands are high.” (Pittendrigh 1948 cited by Benzing & Renfrow 1971.)  Furthermore, it is very probable that all ‘airplant’ Tillandsia species use a CAM pathway indicating that they are quite aridity adapted if not among the more extremophile of species.

  Air-plant Tillandsia trichomes often have inverted umbrella-shapes that when dry, fold tightly, permitting increased sunlight levels onto leaf surfaces; hence, improving photosynthesis.  Conversely, when wet, they rapidly expand and flatten, trapping water along with its dissolved nutrients, which is then rapidly absorbed by especially large water-storage cells lying immediately below a leaf's outer epidermis.  It is then distributed by cellular osmosis to wherever it is needed within the plants.

Nutrient intakes of the more extreme air plants are principally derived from airborne dusts, aerosols and gasses; however, there is ever emerging evidence that various microscopic life forms living on the trichome-coated, hence rough-surfaced leaves of tillandsias, help to provide them with essential nutrients.  For example, certain atmospheric nitrogen (N2) fixing cyanobacteria (so called blue-green algae) and other microflora/fauna.  (Puente & Bashan 1984 & Brighigna et al. 1992.)  In addition to these sources, tree living species will also obtain some nutrients from organic derived leachates flowing down their supports during precipitation events.  However, nutrient levels within the tissues of sampled plants have proven to be remarkably low. (Mez 1904, Penfound & Deiler 1947, Biebl 1964, cited by Benzing & Renfrow 1971.)  These are incredibly resource-efficient, life forms.

  The particularly ant-friendly Tillandsia species that mostly concern us, are with few exceptions, tankless species that mostly prefer somewhat arid, open-canopied, arboreal or very occasionally saxatile (rocky) habitats.  Certainly, they are mostly obligated to non-terrestrial sites, easily rotting if planted in damp soils.  Yet T. flexuosa an often extreme epiphyte grows terrestrially in certain coastal habitats in Venezuela.

  Most myrmecophyte tillandsias have broad bases called sheaths on their otherwise generally lanceolate (lance shaped) leaves.  Leaf sheaths are hemispherical and fit together somewhat like the swollen, tightly compressed leaves that constitute true bulbs. Here however, sheaths are thin in cross section and somewhat domed so that each creates a hollow space sufficient collectively to shelter substantial ant colonies.  The sum of these semi-hollow leaf structures is termed a pseudobulb.

  Yet some Tillandsia species have what botanists consider are true bulbs and some of these are also ant-house plants; however, although these species also create hollows behind leaf sections, here they are situated above the solid bulbous base.

  Pseudo-bulbous Tillandsia and a few other quite similar species fit well within the category of ant-house plants but many other bromeliads including some tillandsias merely provide unspecialised homes for generalist ant species that will nest wherever a suitable arboreal space is found.  Another category of myrmecophyte bromeliad species may best be described as ant-garden mutualists but there are overlaps between all of these groupings.

  According to Gardner (1986) Tillandsia subgenus Tillandsia consists of five groups. Within Group one, she recognized a subgroup of 12 species, whose most important synapomorphy was a pseudobulb. Another species with a pseudobulb is T. intermedia. Gardner did not include this species in the pseudobulbous subgroup but it should have been.  Hence, there are 13 known pseudobulbous tillandsias.  All are epiphytes that live in at least somewhat xeric habitats from sea level to 2,000 m (6562 ft.) in the southern USA, Mexico, Central America, and northern South America.  They are T. ariza-juliae, T. baileyi, T. balbisiana, T. bulbosa, T. butzii, T. caput-medusae, T diguetii, T. intermedia, T. paucifolia, T. pruinosa, T. pseudobaileyi, T. seleriana and T. streptophylla. Among them are two forms. The first type consists of an almost circular leaf sheath that constricts abruptly at the union with the leaf blade as in T. ariza-juliae, T. baileyi, T. bulbosa, T. butzii, and T. seleriana. In the second type, the leaf sheath is broader than the blade but the constriction is gradual and the leaf blade is laminar and involuted as in T. balbisiana, T. caput-medusae, T. diguetii, T. paucifolia, T. pruinosa, T. pseudobaileyi, T. streptophylla and T. intermedia.

  Tillandsias frequently acquire very attractive and long lasting stem and ‘leaf’ (technically bract) colours around flowering times, something they do easily and regularly.  Indeed, they are often worth growing for their beautiful flowers alone. Nevertheless, these highly unusual and interesting plants including the ant-house species are naturally aesthetic and attractive even without flowers.

  There are diverse cultivation needs across the entire genus, but the highly specialised subjects of these notes will have somewhat similar needs to other ant-house plants as long as their unique bromeliad air plant (or tank) morphologies/physiologies are catered for.  Tillandsias may be easily propagated vegetatively with detached but sufficiently developed offsets and some species will self-seed.

[Derrick]

http://aobblog.com/2013/11/mutualistic-ants-contribute-tank-bromeliad-nutrition/

http://www.esajournals.org/doi/abs/10.1890/09-1534.1