Let's start by putting a list..
Malvaceae Sida abutifolia Mill.
Malvaceae Sida acuta Burm.f.
Malvaceae Sida aggregata C.Presl
Malvaceae Sida angustissima A.St.-Hil.
Malvaceae Sida anomala A.St.-Hil.
Malvaceae Sida arboae Krapov.
Malvaceae Sida ascendens A.St.-Hil.
Malvaceae Sida aurantiaca A.St.-Hil.
Malvaceae Sida blepharoprion Ulbr.
Malvaceae Sida brachystemon DC.
Malvaceae Sida brittoni León
Malvaceae Sida castanocarpa Krapov.
Malvaceae Sida caudata A.St.-Hil. & Naudin
Malvaceae Sida caulorrhiza Krapov.
Malvaceae Sida cearensis Ulbr.
Malvaceae Sida centuriata Clemente
Malvaceae Sida cerradoensis Krapov.
Malvaceae Sida chapadensis K.Schum.
Malvaceae Sida coradinii Krapov.
Malvaceae Sida cordifolia L.
Malvaceae Sida emilei Hochr.
Malvaceae Sida ferrucciana Krapov.
Malvaceae Sida galheirensis Ulbr.
Malvaceae Sida gertiana Krapov.
Malvaceae Sida glaziovii K.Schum.
Malvaceae Sida glomerata Cav.
Malvaceae Sida glutinosa Comm. ex Cav.
Malvaceae Sida goyazensis K.Schum.
Malvaceae Sida gracillima Hassl.
Malvaceae Sida harleyi Krapov.
Malvaceae Sida hatschbachii Krapov.
Malvaceae Sida honoriana Krapov.
Malvaceae Sida itaparicana Krapov.
Malvaceae Sida jussiaeana DC.
Malvaceae Sida laciniata Bovini
Malvaceae Sida leitaofilhoi Krapov.
Malvaceae Sida linearifolia A.St.-Hil.
Malvaceae Sida linifolia Cav.
Malvaceae Sida lonchitis A.St.-Hil. & Naudin
Malvaceae Sida luschnathiana Steud.
Malvaceae Sida macaibae Mont.
Malvaceae Sida macropetala Mont.
Malvaceae Sida marabaensis Mont.
Malvaceae Sida martiana A.St.-Hil.
Malvaceae Sida meloana Krapov.
Malvaceae Sida meridiana Fryxell
Malvaceae Sida monteiroi Krapov.
Malvaceae Sida multicrena Hochr.
Malvaceae Sida nemorensis Mart. ex Colla
Malvaceae Sida paradoxa Rodrigo
Malvaceae Sida petropolitana Mont.
Malvaceae Sida pires-blackii Mont.
Malvaceae Sida planicaulis Cav.
Malvaceae Sida plumosa Cav.
Malvaceae Sida potentilloides A.St.-Hil.
Malvaceae Sida pseudo-potentilloides Mont.
Malvaceae Sida pseudorubifolia Krapov. & Bueno
Malvaceae Sida regnellii R.E.Fr.
Malvaceae Sida reitzii Krapov.
Malvaceae Sida rhombifolia L.
Malvaceae Sida rhombifolia var. canariensis (Willd.) Griseb.
Malvaceae Sida rhombifolia L. var. rhombifolia
Malvaceae Sida rivulicola Ulbr.
Malvaceae Sida rubifolia A.St.-Hil.
Malvaceae Sida rufescens A.St.-Hil.
Malvaceae Sida rupicola Hassl.
Malvaceae Sida salviifolia C.Presl
Malvaceae Sida sampaiana Mont.
Malvaceae Sida santaremensis Mont.
Malvaceae Sida schumanniana Krapov.
Malvaceae Sida serrata Willd. ex Spreng.
Malvaceae Sida serrata var. abscissa K.Schum.
Malvaceae Sida serrata Willd. ex Spreng. var. serrata
Malvaceae Sida setosa Mart.
Malvaceae Sida simpsonii Krapov.
Malvaceae Sida spinosa L.
Malvaceae Sida subcuneata A.St.-Hil.
Malvaceae Sida surumuensis Ulbr.
Malvaceae Sida teresinensis Krapov.
Malvaceae Sida tuberculata R.E.Fr.
Malvaceae Sida uchoae Mont.
Malvaceae Sida ulei Ulbr.
Malvaceae Sida ulmifolia Mill.
Malvaceae Sida urens L.
Malvaceae Sida vallsii Krapov.
Malvaceae Sida viarum A.St.-Hil.
Malvaceae Sida xavierii Mont.
Sida rhombifolia foliage looks close, and flowers have the red parts to the anthers but I'm not sure about the petal shape..
http://src.sfasu.edu/~jvk/Pine...
There seems to be variation in both leaves and flowers, I'm trying to look only at scientific sites..
http://www.iewf.org/weedid/Sid...
http://www.tropicos.org/ImageS...
I found a photo of Sida rhombifolia on an Argetina site which is richer in colour but does show signs of the red parts in the anthers. It could be that yours was at a later stage as there's not much pollen showing.. it has a very upright habit.
http://www.floraargentina.edu....
I found this site when looking for the yellow flowered tree, you can search for families then species. I was checking those which are in both Brazil and Argentina, they are not far apart!
http://www.floraargentina.edu....
