\documentclass[a4paper,12pt]{report}

\usepackage{tikz}
\usetikzlibrary{matrix}
\usepackage{booktabs,etoolbox}

\tikzset{leer/.style={}}
\newcommand\verbindungslinieOHNE[3]{
	\foreach [remember=\p as \lastp (initially #2)] \p in {#3}
	\draw[#1](\lastp.east)node[leer]{}-.(\p.east)node[leer]{};
}

\begin{document}

\begin{table}[!tbph]
	\centering
	\caption{Morphologischer Kasten}
	\begin{tikzpicture}[
		nodes={inner sep=3pt}
		]
		\matrix[
		matrix of nodes,
		column 1/.style={anchor=west},% 1.Spalte rechtsbündig
		column 2/.style={anchor=center},
		column 3/.style={anchor=center},
		column 4/.style={anchor=center},
		column 5/.style={anchor=center},
		column 6/.style={anchor=center},
		](m){
		Test
		& Test
		& Test
		& Test
		& Test \\
		        
		Testp
		& Test
		& Test
		& Test
		& Blub \\ 					
		
		Test
		& Test
		& Test
		& PfPfPfp
		& Test \\ 	
		
		Testfunktion
		& Test
		& Test
		& Test
		& Test \\ 		
		};
		
		% Kopfzeile
		\node(ul)[anchor=south west] at (m.north west) {Teilfunktion};	
		\foreach[count=\i from 2] \c in {1,2,3,4} \node[anchor=base] at (ul.base-|m-1-\i){\c};
		
		
		% Tabellenlinien
		
		\draw[line width=\lightrulewidth]
		([yshift=0]ul.south-|m.west)
		--([yshift=0]ul.south-|m.east);
		\draw[line width=\heavyrulewidth]([yshift=0]ul.north-|m.west)
		--([yshift=0]ul.north-|m.east)
		([yshift={0}]m.south west)
		--([yshift={0}]m.south east);
		
		% Verbindungslinien
		\verbindungslinieOHNE{black}{m-1-5}{m-2-4,m-3-4,m-4-4}

	\end{tikzpicture}
\end{table}
	
\end{document}