cordate) base, Aristolochia A mesiana is also sharply dis- 
tinct from most other species, approaching, amongst the 
South American representatives, only A. maxima Jac- 
quin from which it differs markedly in the texture of 
the leaves, structure of the inflorescence and in floral 
characters. 
In the key to the subgeneric sections of Aristolochia 
which Hoehne has published (Flora Brasilica 15, pt. 2 
(1942) 25), Schultes & Lopez 9296 traces out to his sec- 
tion Mestipulatae (devoid of pseudo-stipules), sub-section 
Euunilabiatae (flowers unilabiate, or with the lip usually 
not surrounding the mouth of the tube but developed on 
one side alone). Aristolochia A mesiana does not approach 
any of the concepts included in these sections, resembling 
A. disticha Masters, a species known only from the Rio 
Tapajoz in Amazonian Brazil, in having an extremely 
abbreviated racemose inflorescence. 
In addition to the extraordinarily coriaceous and bas- 
ally rounded leaves, Aristolochia A mesiana exhibits sev- 
eral other characters which are either rare or unknown in 
the genus. The curious triangular indentation or incision 
at the apex of the lip is much deeper and more strongly 
marked than in any other known South American spe- 
cies, although a similar condition is seen in Aristolochia 
Macbrideana Standl., 4. Hggersi Hoehne and A. pap- 
illaris Mast. The column of Aristolochia Amesiana is 
unusually short in relation to the length of the tube, a 
condition seen in few of the South American species. In 
life, the leaves have a blue or steel-green sheen which, so 
far as I have been able to ascertain, has not been reported 
for other species. 
[t is obvious that Aristolochia A mesiana, like all other 
plants of the caatingas of the upper Rio Negro, is highly 
adapted to xerophytic conditions. It climbs in the low, 
light, semi-open groves of Hevea paucifiora var. coriacea, 
[ 189 ] 
