from what I could find on the net, the picture environment does not offer the triangle shape. It is possible to get something similar with lines but not when you want the triangle to be fill up with a solid color. Do you confirm? Maybe the bezier curves could be an option.
\setlength{\unitlength}{2pt}
\begin{picture}(50,200)
\linethickness{1pt}
\bezier{20}(0,0)(10,30)(50,30)
\put(0,0){\circle*{1}}
\put(50,30){\line(-1,0){40}}
\put(50,31){\makebox(0,0)[b]{C}}
\end{picture}