One of the difficulties within the botanical and scientific fields is categorization and deciphering between variety, sub-species, species, genera and sometimes even among plants in different families because the specific types of differentiating indicators used to tell them apart may not be readily available such as flowers and/or seeds. The environmental conditions may or may not be ideal for the characteristics to reveal themselves as is the case for why many sub-species & varieties sometimes develop. Another thing that creates misunderstandings is the use of the same common name for many different specimens.
Here are just some of the differentiators and indicators to help distinguish between the most commonly used:
1. 'Indian Bitter Neem' Azadirachta indica
2. 'Sentang Jack' Azadirachta excelsa
3. 'Super Thai Neem' Azadirachta indica spp. siamensis (sub-species)
4. 'Chinaberry' Melia azedarach
'Chinaberry' Melia azedarach: In the early months of 2016 we first heard about people confusing the Melia azedarach for Indian Neem. One historical point to bring up is that as scientist, botanist & professional horticulturists come to a general conclusion about plants they do get reclassified and at one point the now Azadirachta indica used to be categorized and so named Melia indica. Otherwise, there really shouldn't be an issue visually recognizing the two if they are next to each other. Any person familiar with the true Neem would not have a problem telling the difference between the two. Melia azedarach shows bi-pinnate or even tri-pinnate leaves vs single for Azadirachta indica. Below are leaflet photomicrographs provided by Revista Internacional De Botanica Experimental / International Journal of Experimental Botany (Source) taken using a Reichert Microstar IV microscope at the Plant Taxonomy Research Laboratory, Botany Department, Faculty of Science, Ain Shams University, Cairo, Egypt.
Photographs illustrating foliar characteristics of Azadirachta indica (a,c,e,g,i) and Melia azedarach (b,d,f,h,j).
'Super Thai Neem' Azadirachta indica spp. siamensis (sub-species) :
There is still discussion whether the taller neem trees with obvious larger leaves and seeds, longer flowers and much taller trunks of Thailand are another species or sub-species. These Thai trees sometimes exhibit red or white flowers. We believe the latter as all other traits are similar except strength/concentration of chemical properties along with physical attributes are more pronounced and again larger and taller than Indian neem (A. indica) and for that reason you'll often see its name written Azaditachta indica spp. siamensis. A study of pollen morphology and isozyme-patterns was completed Boonsermsuk & Jitjamnong, (1989). In this study, 3 distinct varieties of the species were found based on pollen study conclusions. That 3rd variety with distinct characteristics was labeled Sadao Thiam, aka Sadao Chang, aka Azadirachta excelsa (Jack). The two seemingly more similar varieties only differed in thickness of their pollen membrane, but all other pollen characteristics remained the same. A. indica spp. siamensis ocurred naturally in moist deciduous forests not dry areas as where most A. indica can be normally found. (Source: Food & Agricultural Organization of the United Nations. http://www.fao.org/docrep/006/u5380e/U5380E08.htm)
'Sentang', 'Marrango', 'Philippine Neem', Azadirachta excelsa (Jack), Azadirachta intergrifolia, (species): A major differentiating characteristic from Indian neem is found in the leaves of this species. Leaflets are elliptical, asymmetrical with entire margin (not serrated as in Indian Neem). Flowers are also a greenish white. Indian neem leaves are imparipinnate (terminal unpaired), containing eight to 19 leaflets per leaf, simple teeth order and about two teeth per centimeter.
Fruits, flower and flowering branch of Azadirachta excelsa (Jack). From: Plant Resources of South-East Asia No. 5:2.
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