I'm not a specialist or knowledgeable about porcelain, but as far as checking with internet, what JimmySeal san explained is all about it.
錦山 (most likely it is pronounced kinzan, not nishikiyama though I'm not 100% sure) is a name of 九谷焼 kutaniyaki (kutani porcelain) workshops - workshop is usually called 窯 (kama/kilm) or 窯元 (kamamoto - sometimes people from the workshp is also called kamamoto).
錦山窯 was founded by 庄作 in Meiji 39 (1906), which was succeeded by 清一.
吉田美統 (yoshida minori 1932~) is the 3rd and current 錦山.
He succeeded the kiln in 1951, and is now a "national important intangible cultural heritage".
There are three artists including 吉田美統 at 九谷錦山 - 吉田美統, 吉田幸央, 吉田るみこ. It seems that the works by individual (his original) is marked 九谷美統 while traditional works of the kiln is marked 九谷錦山.
Your plate is marked 九谷錦山 and the box also does not show whose work it is, it just indiates the plate is from 錦山窯. It could be by 吉田美統, but again I'm not sure...
About 錦山窯
http://store.yahoo.co.jp/hokusando/a1dac1f7ce60.html
作家紹介 - 錦山窯/吉田美統・幸央・るみこ - 陶芸の店 もと子
Works by 吉田美統
http://www.kutani.co.jp/shouhin/sakka/minori/774-12.php
【楽天市場】エラー
Marking of Kutani porcelain (see 25 and 26)
List Kaku
I hope someone who really knows about Kutani will tell you more about it and give you accurate information.
