My name is Tracy Kahn, and Dr. Mary Lu Arpaia asked me to provide you with some information about this topic.  I am the curator of one of the most diverse collections of Citrus and Citrus relatives here at the University of California – Riverside.  I also conduct research on new cultivars of citrus that are imported into California and the US.  In addition the Citrus Variety Collection has a website (http://www.citrusvariety.ucr.edu) that I thought you might like to know about since you are asking questions about Clementines and Mandarins.

Mandarins refer to a group of cultivars and includes Clementine and Satsuma and many other mandarins.  There are actually many selections of Clementine mandarins and some are more commercial than others with Clemenules Clementine being the most commercially grown of the Clementine mandarins.  If you have heard of “Cuties” they are a marketing name used to pack Clementine mandarins before Christmas generally and W. Murcotts and Tango mandarins after the holidays.  The word tangerine is often used interchangeably with the word mandarin but actually the term tangerine was coined for brightly colored sweet mandarins that were originally shipped out of the port of Tangiers Morocco to Florida in the late 1800s and the term stuck.  Below this email note is the link and a section from the Citrus Industry Volume I Chapter 4 about mandarins.  Another interesting thing about mandarins is that we now know that there were three basic citrus types (mandarin, citron and pummelo) and that others that we think of as basic types or species (sweet oranges, sour oranges, grapefruits) are actually ancient hybrids or backcrosses of theses. Also, many of the cultivars that we think of as mandarins or tangerines may in fact not be true mandarins, but actually mandarin hybrids.

                                                                         --Tracy L. Kahn, Ph.D.

http://websites.lib.ucr.edu/agnic/webber/Vol1/Chapter4.html  Citrus Industry Volume I Chapter 4

THE MANDARlNS
      Principal in importance in the Orient are the mandarins, a large, distinctive, and highly varied group that includes some of the finest and most highly reputed citrus fruits.  Closer in resemblance to the oranges than to any of the other groups, these fruits are commonly referred to as mandarin or loose-skin oranges—a usage which is both unfortunate and confusing in view of the numerous, highly distinctive differences between the two groups.  In the United States, where the name tangerine first came into common usage, mandarin and tangerine are used more or less interchangeably to designate the whole group.  Since mandarin is the older and much more widely employed name, its use is clearly preferable.  Presumably because of the orange-red color of the Dancy variety, which originated in Florida and was introduced in the markets as the Dancy tangerine, horticulturists have tended to restrict the use of the term tangerine to the mandarins of similar deep color.  However, this is a usage of convenience only and the tangerines do not comprise a group of natural significance.  The mandarin is the mikan of Japan, the suntara or sangtra (numerous modifications) of India, the mandarino of Italy and Spain, and the mandarine of French-speaking countries.
      While the range of variation in characters exhibited by the mandarin group is much greater than in the oranges or pummelos and grapefruits and the existence of a number of species is indicated, the distinctive features of the group as a whole are as follows:
      Fruit very small to medium (prevailingly smaller than the oranges), oblate to highly compressed form; rind and fruit sections loosely adherent (more so than any of the oranges); open core (much more so than any of the oranges); flavor and aroma commonly distinctive; seeds with greenish cotyledons (minor exceptions).
      Tree very cold-resistant (more so than any of the oranges) but fruit not; distinctive leaf petioles (wings line-margined with few exceptions); blade notch-pointed and with main vein prominent above as well as below; spines small and few or lacking; flowers single or in unbranched inflorescences and prevailingly small (minor exceptions).
      That the mandarin probably originated in northeastern India is strongly suggested by the existence in the forests of Assam of a primitive form, Citrus indica Tan., the so-called Indian wild mandarin, together with numerous mandarin hybrids and other and more highly developed forms not found elsewhere.  It seems clear, however, that the King and Kunenbo mandarins must have originated in Indo-China and it is virtually certain that the satsuma mandarin had its origin in Japan.  South China must also be the region of origin of some of the numerous mandarins.  Finally, there is considerable reason for concluding that the Mediterranean mandarin, as the name indicates, originated under cultivation in Europe, presumably in Italy.
      According to Webber (1943), the first mention of the mandarin in Europe relates to the introduction into England by Sir Abraham Hume in 1805 of two mandarins from Canton, China, one of which was described and illustrated in 1817 in the Botanical Register and the other in 1824 in Andrews Botanical Repository.  Ziegler and Wolfe (1961) have concluded that one of these introductions was the highly reputed ponkan.  That the mandarin had reached the Mediterranean basin somewhat earlier seems likely, however, for Risso and Poiteau (1818-22) mention a "mandarin orange" which had been known there "for some years" and Chapot (1962c) assigns the date of origin of the Mediterranean mandarin as between 1810 and 1815.  From the fact that in 1830 the village of Monroe on the St. Johns River in Florida changed its name to Mandarin, Ziegler and Wolfe (1961) concluded that this fruit must have been introduced into the United States about 1825.  The fates of that introduction and of another known to have been made in 1838 are obscure.  The first known successful introduction is said to have been made by the Italian consul at New Orleans between 1840 and 1850 and consisted of the Mediterranean mandarin, which came to be known as Willowleaf in this country (sometimes erroneously called China).