I called it 'mean' because it causes severe burns to the skin when accidentally touched or brushed against. My friend got a serious rash on her upper arm that lasted for several days. The plants can grow very tall, some were over 2m, none of them was in bloom the time I was there.
The toothed leaves are a shiny dark green and big.

My first instinct is the Nettle family Myriam, given the serious rash! The leaves do resemble a large nettle.

Look at Urera baccifera ..

https://sites.google.com/site/...

http://en.wikipedia.org/wiki/U...

http://biogeodb.stri.si.edu/bi...

The leaves appear to be broader in some, look at the lower smaller part of the plant in this link, there's several photos ..

http://herbaria.plants.ox.ac.u...

The photo on the following link is in the Tropical plants, Brazil, the stem looks ridged without spines ..

http://fm2.fieldmuseum.org/pla...

Urera nitida is in the location too ..

http://www.ufrgs.br/fitoecolog...

Another very different pic of the same species on the same site!

http://www.ufrgs.br/fitoecolog...

http://www.biodiversidade.rs.g...

Thanks Janet!

My first instinct was also a related family member of the Stinging Nettle! I even did a search with that but had no results. The burns caused by this plant are much more severe than the Stinging Nettle and last much longer! The skin of the upper arm of my friend looked horrible, full of reddish inflamed bubbles. It took more than a week before it eventually and slowly cured!

The majority of the pictures of Urera baccifera from the links don't show the shiny dark green leaves, I couldn't see any visible hairs on the leaves on my plant's leaves either, there might have been but I didn't risk to come too close to inspect that!
I also think the stem had no spikes but was smooth, a bit purplish and ridged like you saw.
So maybe Urera nitida is a better candidate..

The photo I linked to of Urera baccifera in the last link, the fieldmuseum, doesn't look to have spines on Myriam. I clicked on the link for herbarium specimums. there's different leaf shapes there from different locations ..

http://fm1.fieldmuseum.org/vrr...

Clicking from a link from the herbarium brings you back to several photos of the live plant.

http://fm2.fieldmuseum.org/pla...

Spines on some plants are barely noticeable, I imagine if there was small spines on your plant they wouldn't show unless you have a closer shot.

Urera nitida isn't listed on that site.

Urera baccifera is accepted on the Plant List, but is in review. It also has synonyms giving different varieties which suggest it does vary.

http://www.theplantlist.org/tp...

Urera nitida is also accepted, but in review.

http://www.theplantlist.org/tp...

Could they both be variations of the same plant?

Info on Urera baccifera ..

http://www.scielo.sa.cr/scielo...

Urera nitida .. the first photos show a stem with no visible thorns, the next ones do have thorns! It's from 'Universidade de São Paulo'.

I think the new stems may not have thorns, where older stems do from looking at the photos. It's interesting to note they haven't listed Urera baccifera in the side menu.

https://sites.google.com/site/...

Description translated:

Shrubs 0.8 -3 m alt. Ramos -0.5 cm ø 0.3., pubérulos, stinging trichomes sparse arrays. Blades 6-22 x 2-9 cm, lanceolate, membranáceas; adaxial face lisa, glabra; cistólitos concentrated near the ribs; adaxial face lisa, bright, cistólitos glabra, distributed throughout the limbo; acute, Apex acuminate; acute base; entire margin sparsely bite; 6-10 pairs of secondary veins; Stipules 5-7 mm compr., triangular, bífidas, conadas, deciduous, pubérulas; petioles (2-) 5-15 cm compr., striated, glabros. Inflorescences axillary, 1-3 cm compr., vináceas, asymmetric, pubescent, in spite of stinging trichomes; 5-8 mm interflorais bracts compose; flowers estaminadas 4-5-lobed, sessile or (sub) sessile; lobes 1-1.5 mm; stamens 5. Pistillate flowers 4-lobed, lobes 0.5 -0.8 mm; stigma penicilado. Achenes oval-rounded, 2-3 mm dia., symmetrical, gnarly, surrounded by fleshy perianth add, rosea to Titian in maturation. Oval seeds, ridged; elliptical cotyledons; straight embryo.

It is confusing Janet, the photo material on the web often contradicting.

The pictures of 'Universidade de São Paulo' of Ucera nitida don't convince me, it doesn't feel right but reminds me of another plant I also photographed, I had put them in the same folder as they had a lot similarity, but its leaves were not shiny (when dry), more roundish and the teeth smaller, it also looks like the one on this site:
http://www.ufrgs.br/fitoecolog...

I think the one I posted before is Urera baccifera (based on the pictures of the fieldmuseum which must be a reliable source) and the second one Urera nitida, (based on the pics of the 'Universidade de São Paulo')

You had it spot on from the beginning!

There's several photos of Urera baccifera on the page further down of which none show obvious spines Myriam, so yes I think that is it.

http://www.ufrgs.br/fitoecolog...

Your last set of photos do show spines (I think) in the second photo.

Yes, I do think that the second plant had spines, Janet, I should also have taken shots of the stems!

On the site I linked to above:

The leaves and stems of Urera baccifera are covered with stinging hairs

http://www.scielo.sa.cr/scielo...

Fine hairs wouldn't be visible unless you took very close shots Myriam, that is what would do the stinging.

Yes, thanks Janet, I did look at the link but found the experiments on the poor rats and mice very creepy that's why I didn't read further on!

And yes, it is very possible that the leaves of Urera brassifera were covered with very fine hairs, I actually didn't dare to come very close to the plant for known reasons!