Plant Geography Greenhouse Tour #1

Plant Geography
Botany 422- 2024

Greenhouse 2 (Tropical House)
1. Vachellia collinsii (Acacia collinsii) — bull-horn acacia (Fabaceae)
• A famous mutualism, especially in tropical savanna or dry forest biomes: the acacia provides food
and shelter for ants, which in turn protect the plant from herbivores. The shelter is in the form of
hollow, stipular thorns. The food is in the form of “Beltian bodies”, little globs of oil and protein at
the tips of leaflets (look closely). These are named for the “Naturalist of Nicaragua”, Thomas Belt.
Acacia s.l. has been shown to be polyphyletic and was subsequently split into five different genera.
“Acacia” can still be used as a common name but as a genus name now only refers to a number of
Australian species.
2. Ficus binnendjikii —fig tree (Moraceae)
• Many species in this large genus (ca. 800 species), are strangling species. The genus is found in all
three wet tropical floristic regions. They often start as an epiphyte and slowly surround and
suffocate the host tree. Although not attached to a host, you can see this plant is pushing down
spiralling roots as if it was on a host tree. All figs are pollinated by wasps and, as in the orchids with
euglossine bees, a particular species of fig wasp often has coevolved to pollinate a particular species
of fig.
3. Osmanthus heterophyllus — holly olive (Oleaceae)
• This genus in the olive family is mostly native to warm, wet temperate or subtropical humid forests
but with one species (O. americanus) in the southeastern United States, from Texas to Virginia. This
biome type is often characterized by tough, evergreen leaves adapted to year-round growing
conditions but with marked seasonality in temperature. Similar leaves with sharp prickles (“holly”-
leaves) can be found in the Mediterranean biome as adaptations to marked seasonality in moisture
Greenhouse 3 (Orchid House)
4. Adenium obesum — desert rose (Apocynaceae)
• This species occupies African dry thorn forests south of the Sahara Desert. The stem enlarges as it
grows, storing large quantities of water. You can see the large (“obese”) caudex or rootstock. All
members of the family, including the milkweeds, have a well-developed latex system for protecting
its costly parts from herbivores. In dry winter conditions, the evergreen leaves can drop.
5. Myrmecodia sp. — ant plant (Rubiaceae)
• A genus of epiphytic myrmecophytes (“ant plant”) native to Southeast Asia and Australia. A second
genus, Hydnophytum, can be seen next to this plant. They form a symbiotic relationship with ants.
Ant plants provide habitats for ant colonies high up in the wet tropical forest canopy, protecting
them from the elements and predators – see the tiny holes that this plant is forming in the thickened
stem base. Ants likewise provide defense for the plant, prevent tissue damage, and also provide
nutrients to the plants by leaving wastes within tunnels inside the caudex. Special glands lining the
tunnels then absorb nutrients for the plant.
Greenhouse 4 (Tropical House with pond)
6. Cyathea sp.— tree fern (Cyatheaceae)
• Tree ferns are found in all tropical areas of the world and often form a conspicuous component of
wet tropical rainforests, especially the high-elevation cloud forests, and in the Southern Hemisphere
temperate rainforests as well. The genus Cyathea is pantropical in distribution with over 470
species. This species is from tropical New Guinea and Queensland, Australia. Tree ferns may grow up
to 10 m tall but their trunks are not made up of wood. All new growth is supported by old leaf bases.
Note the conspicuous way in which the new leaf “fiddlehead” emerges, characteristic of most ferns.
This is called circinate vernation.
7. Platycerium bifurcatum — staghorn fern (Polypodiaceae)
• This epiphytic fern grows in wet tropical forests the Old World. As the leaves of the plant die, they
remain attached to the base of the plant. As the dead leaves accumulate, they form humus at the
base of the plant, catching and storing water and nutrients – a “trash basket” into which roots can
penetrate. If you look peer in closely, you can see the adventitious roots inside the scales. These
large “baskets” at the base of the plant are capable of holding gallons of water. Another species of
“trash basket” and epiphytic fern is hanging by the pond several feet away.
8. Rhizophora mangle — red mangrove (Rhizophoraceae)
• The dominant mangrove in the Neotropics, especially prevalent close to the sea. Just to the right is
the amphi-Atlantic (east S. America, west Africa) Avicennia (white mangrove) in an unrelated family
Acanthaceae. Some adaptations to the halophytic lifestyle have convergently evolved: these include
tough, evergreen leaves, prop roots (red mangrove shows it here), viviparous seedlings, and
pneumatophores (aerial roots – white mangrove shows it here).
Greenhouse 5 (Begonia House)
9. Tillandsia — Spanish moss (Bromeliaceae)
• The morphologically most unspecialized (but ecologically still specialized) members of the almost
strictly Neotropical family Bromeliaceae are terrestrial xerophytes (Puya, Pitcairnia and Ananas, the
pineapple) found in a diversity of biomes. Intermediate in morphology are the tank epiphytes that
use overlapping leaf bases to catch and store water (Vriesia, Neoregelia). The most specialized are
the extremely modified epiphytic Tillandsia species, which are covered with absorptive scales to trap
water in the canopy and lack root systems, at least as adults. Spanish moss is a species very reduced
relative to its related species growing next to it and is sometimes called an “atmospheric” epiphyte
as water is mainly obtained from the air.
Greenhouse 7 (Succulent House)
10. Bursera simaruba — gumbo-limbo, turpentine tree (Burseraceae)
• A genus of 100 species, restricted to the Americas. This species occurs in dry subtropical or summer
green forests of southern Mexico and Guatemala. This plant is deciduous; notice the dried up
compound leaves and very tiny buds that will leaf out as the dry season ends. Note the green bark,
an adaptation to seasonally dry subtropical forests when green leaves have dropped in the winter
11. Euphorbia spp. — spurges, poinsettia (Euphorbiaceae)
• This genus contains ca. 2,000 species and is cosmopolitan. There are many species from Africa and
Madagascar (on display here) that resemble cacti found in deserts. What xerophytic adaptations do
they share? Although some spurges are extremely similar (convergent!) to cacti, it is very easy to
differentiate the two, even when not in flower. Prick a spurge stem and then a cactus stem. What
do you notice (latex)?
12. Opuntia spp. — prickly pear cactus (Cactaceae)
• Cacti are a large family (2,000 spp.) almost entirely restricted to the New World. They are famous as
a symbol of the American deserts. Most species have swollen, fluted stems that hold water during
long periods of drought. Some species are giant columnar “trees”, some are multi-branched shrubs,
others have globose stems, and still others, are tropical epiphytes with flattened stems. To cope
with life in such arid and sunny environments, cacti have evolved CAM (Crassulacean acid
metabolism) photosynthesis, which allows them to reduce water loss during the day. CAM
photosynthesis has evolved multiple times in plants including in Bromeliads (see Tillandsia above).
There are two species of cacti native to Wisconsin! The epiphytic African Rhipsalis – the only non-
American native cacti – can be seen by the windows.
Greenhouse 8 (Tropical High House)
13. Theobroma cacao — cacao, cocoa bean tree (Malvaceae)
• This species is native to wet tropical forests of the Americas. Note the large, evergreen leaves. As
with some non-canopy rainforest trees, the tiny, purplish flowers are cauliflorous – literally “stem
flowering” – which are pollinated by midges. Fruits of various stages are seen here. Seeds of cacao
are used to make chocolate and a favorite food of one group of fruit dispersers – monkeys. There are
a couple of other wet tropical tree species in this High House that exhibit cauliflory (but not
flowering now) and some are bat pollinated.