Alemow (Citrus macrophylla)

Introduction

Alemow is a variety of Citrus that is said to be native to Cebu, Philippines. It’s also sometimes called by the name ‘Colo’ or ‘Alimau’. It is mostly useful as a Citrus rootstock, while also being able to produce an edible crop.

We imported Alemow seeds into New Zealand in early 2025 and sold them to the public, making this the first release of Alemow in New Zealand. This article includes all the latest information about Alemow and its behaviour that we can find. Eventually we will update this article to include results of its performance in New Zealand as well once that information is available.

Botany

The life of Alemow starts with a seed. Alemow has highly polyembryonic seeds and so the vast majority of seedlings are nucellar clones [1]. The way this essentially works is that the mother plant inserts additional embryos into the seed that are clones of the mother. These embryos are usually much larger than any zygotic (hybrid) embryo, and so they usually outcompete the zygotic embryo. What this means in practice is that something like 95%~ of Alemow seedlings are exact clones of the mother plant, and so we can be certain that we have imported the exact Alemow variety from overseas, and not just something similar.

Alemow grows as a vigorous small tree with a spreading habit and many short spines. Flowers and new growth are both strongly purple-tinted, and the crushed leaves smell like lemon. Leaves are medium sized with a small winged petiole.

The fruit are medium large, seedy, and with a rough and bumpy texture. Taste is discussed later in the article.

Picture of Alemow fruit sourced from [2]

Genetics

The latest genetic evidence clearly shows that Alemow is a direct hybrid between a papeda seed parent and a citron pollen parent. This is the same hybrid formula (Citrus micrantha x medica syn. Citrus x aurantifolia) as Mexican / Key lime, and so Alemow can correctly be considered as a true giant lime [3].

Partial Citrus phylogeny highlighting Alemow’s parentage. Adapted from [3].
Genetic composition of Alemow (Citrus macrophylla). Adapted from [3]

Previously it was suspected by Swingle and Reece that Alemow was a hybrid of Celebes papeda (Citrus celebica) and pomelo [4]. This suspicion has been spread widely and followed Alemow everywhere. We even repeated it in our initial descriptions. While there is definitely no pomelo parentage in Alemow, as far as I can tell it can’t yet be ruled out that Celebes papeda is the mother. Future genetic work should be able to clarify the exact parentage down to the individual variety.

Working from the hypothesis that Alemow is native to the Philippines, it is difficult to find any info on whether citrons are native to the Philippines or not. I can find a cryptic reference to an old synonym of citron called ‘Citrus alata‘ described by Tanaka, that may have had the type specimen collected at Mount Apo in Mindanao, Philippines if I’m reading things correctly [5]. Again future genetic work should be able to provide a clearer picture of the exact parents of Alemow.

Rootstock I

Alemow has many positive characteristics as a rootstock, and a few very negative characteristics. I had originally noticed that Alemow was used as a rootstock in the Givaudan Citrus Variety Collection at the Unversity of California Riverside [UCR]. This is the list of varieties currently accessioned on Alemow rootstock:

  • Taylor Eureka lemon
  • Bearss lime
  • Limonero Fino 49 lemon
  • Lima Criolla Rangpur lime
  • Limonero Messina lemon (CRC 4121)
  • Seedless Lemon
  • Mitha-Tulia limetta
  • Limonero Fino Largo 95 lemon
  • Atalantia zeylanica
  • Mexican citron
  • Lupe Lisbon lemon
  • Gul-gul lemon hybrid
  • Lunario lemon
  • Microcitrus australasica CRC3672
  • Honghe papeda
  • Genova EEA Tucuman lemon
  • Femminello Siracusano 2KR lemon
  • Citrus hystrix (CRC 3103)
  • Chulo Key lime
  • Giant Key lime

The list is mostly lemons and limes and can give some idea of compatibility. Alemow was furthermore recommended to me to source by David Karp of UCR.

Another one of the reasons I became interested in Alemow was that it’s often recommended as a rootstock for kumquats and other Citrus grown in pots by members of tropicalfruitforum:

User sc4001992 writes:

Kumquats grows best on macrophylla for me. [6]

…

I have 12 citrus varieties grafted on my large macrophylla and no issues so far with compatibilty. The Meiwas grafted on the macrophylla is growing very fast while my other 2 Meiwa purchased from the nursery still hasn’t grown much at all. [7]

User Travillion writes:

My meiwa kumquat is on macrophylla and it is very vigorous. I bought it in the late summer of 2021 and it set fruit in the summer of 2022 that I enjoyed this winter/spring. It has set even more fruit this summer. I can’t speak to longevity because it’s only a few years old, but so far I have had no complaints, it’s my most productive and hardy tree. I contacted the supplier after I bought the tree to find out what rootstock it was on and they said my nursery specifically requests mac, the supplier usually uses a different rootstock (probably poncirus or FD). [8]

User BorisR writes:

I believe that macro is one of the best rootstocks for pot cultivation. Although I myself still have only a couple of grafts on the macrophile. But for everyone who, as I know, has something growing on the macrophile, including kumquats, it all grows very well, without chlorosis and root rot and other problems. [9]

In terms of commercial rootstock usage, Alemow has been trialed in California for lemons and found to give excellent performance (Mac = Alemow) [10]. Here are the graphs for the trial in Santa Paula (warm Mediterranean climate, closest to a New Zealand climate).

For plant health ratings Alemow achieved the best rating.

For canopy volume Alemow achieved second best rating.

For the bud union, Alemow achieved the best rating. The score essentially means there is no benching at all, with a completely smooth bud union. Benching is one way that grafted Citrus trees can decline over time and eventually die. Trifoliata is particularly susceptible to benching with lemons (note it achieved both lowest scores in the trial).

For suckering, Alemow achieved the best rating, with no suckers on average. This is likely a consequence of the bud union being nearly perfect, as suckering is often a response to poor scion-rootstock compatibility.

Alemow achieved the highest cumulative yield, although it should be noted that the difference in yield was mostly due to higher early yields, with later yields more comparable.

Surely there has to be a catch for Alemow to perform so well? And yes, there is…

Citrus Tristeza Virus

Alemow is very susceptible to Citrus Tristeza virus [CTV], as well as having low resistance to nematodes and average resistance to Phytophthora [11]. This susceptibility to CTV is why Alemow is used commercially as a rootstock almost exclusively for lemons, because lemons are noticeably resistant to CTV.

CTV is not really a single virus but a group of hundreds of strains, where each strain has varying effects depending upon the host and multiple strains may be present. Some strains are severe, and some are mild. The effects generally range from dieback, wilting, decline and bud union failure. “Quick decline” is the worst expression where the tree may die in a matter of weeks [12][13].

CTV is widespread in New Zealand being found in nearly 90% of Citrus varieties in one trial, and without a clean budwood scheme it is continually being spread around through infected budwood as well as being retransmitted by Citrus aphids [14]. So for this reason it is best to use Alemow as a rootstock with CTV resistant varieties, or to accept the risks that CTV-susceptible Citrus may eventually perform poorly if grafted on Alemow.

CTV resistant varieties include lemons, trifoliata and its hybrids (citrumelos, citranges, citrandarins), rangpurs, rough lemons (e.g. Kaipara lemon), Kinkoji, wild mandarins (Cleopatra, Sun Chu Sha, Sunki) [15]. Meiwa kumquat is reported to have resistance to multiple strains of CTV [16]. Etrog-type citrons seem to have some resistance to CTV, which may explain why many lemons have CTV resistance [17]. Since Alemow is also a citron hybrid and is not resistant then it does perhaps imply the citron parent of Alemow is not closely related to Etrog citrons.

Rootstock II

Alemow also tends to produce large, early fruit with thicker peels and slightly lower total soluble solids [TSS] than other rootstocks [11]. This is generally not a problem for lemons as slightly lower acidity is usually fine, but it can present a problem for other Citrus grown for sweet fruit (e.g. oranges, mandarins – which reminder are not resistant to CTV). One study however reported that despite the TSS of fruits grown on Alemow rootstock decreasing, the ratio of TSS to acid (essentially the sugar to acid ratio) increased [18].

Perhaps the thicker peel is also useful for kumquats as well, since the sweetness of kumquats is located in the peel?

Alemow has also been found to induce precociousness when used as a rootstock [18].

Lastly, Alemow has very high tolerance to alkalinity and salinity [11]. Alkaline soils are relatively rare in New Zealand, mostly being restricted to the drier portions of the East Coast (where the cold may be too much for Alemow). However saline soils are common everywhere in New Zealand at sites very close to the sea, and so Alemow might find niche use as a coastal Citrus rootstock where other rootstocks suffer from salt-induced chlorosis.

Fruit

The Citrus Industry Volume 1 states [19]:

The fruit has 13 to 16 segments and rather dry, sour pulp, considered inedible even by the natives.

This description seems to be the source for taste descriptions that have followed Alemow wherever it was written about. However it’s not clear if this description is accurate in the first place. There are very few firsthand taste reports of Alemow available. One of the only ones is from forum user sc4001992 on tropicalfruitforum, who writes:

I did try the fruit, it is very acidic and sour. But it is not that bad, no strong smell or taste that is hard to eat or drink. It kinda reminds me of the taste of Key lime. [20]

This is quite an interesting comparison as the user likely did not know that Alemow and Key lime are the same cross. I have personally never tasted Alemow fruit, but I believe that based on the parentage it is most likely to taste similar to Key lime (= Mexican lime). Key lime is generally described as being less acid, more aromatic and a bit more bitter, versus Persian lime.

Lastly it’s possible to use almost any Citrus for marmalade, and Alemow should be no exception. Makrut / Thai lime is used rarely for marmalade, and Alemow should taste better than that due to the citron parentage. We look forward to the day we can try New Zealand Alemow marmalade 🙂

References

  1. https://citrusvariety.ucr.edu/crc3842
  2. https://commons.wikimedia.org/wiki/File:Citrus_macrophylla.jpg
  3. Curk F, Ollitrault F, Garcia-Lor A, Luro F, Navarro L, Ollitrault P. Phylogenetic origin of limes and lemons revealed by cytoplasmic and nuclear markers. Ann Bot. 2016 Apr;117(4):565-83. doi: 10.1093/aob/mcw005. Epub 2016 Mar 4. PMID: 26944784; PMCID: PMC4817432.
  4. https://idtools.org/citrus_id/index.cfm?packageID=1179&entityID=8284
  5. Goldschmidt EE, Bar-Joseph M, editors. The Citron Compendium: The Citron (Etrog) Citrus Medica L.: Science and Tradition. Springer Nature; 2023 Jun 7. Appendix—Formal Classification; p. 32.
  6. https://tropicalfruitforum.com/index.php?topic=54586.msg522186#msg522186
  7. https://tropicalfruitforum.com/index.php?topic=54457.msg522170#msg522170
  8. https://tropicalfruitforum.com/index.php?topic=51518.msg495452#msg495452
  9. https://tropicalfruitforum.com/index.php?topic=51518.msg495502#msg495502
  10. https://ucanr.edu/sites/default/files/2019-10/313407.pdf
  11. https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0017/1313711/Selecting-citrus-rootstocks.pdf
  12. Moreno, P., Ambrós, S., Albiach-Martí, M. R., Guerri, J., & Peña, L. (2008). Citrus tristeza virus: a pathogen that changed the course of the citrus industry. Molecular plant pathology, 9(2), 251–268. https://doi.org/10.1111/j.1364-3703.2007.00455.x
  13. https://auscitrus.com.au/app/uploads/2020/04/Citrus-tristeza-virus-in-Australia.pdf
  14. Harper SJ, Pearson MN. Citrus tristeza virus strains present in New Zealand and the South Pacific
  15. https://edis.ifas.ufl.edu/publication/HS242
  16. Mestre, P., Asíns, M., Pina, J. et al. Efficient search for new resistant genotypes to the citrus tristeza closterovirus in the orange subfamily Aurantioideae. Theor Appl Genet 95, 1282–1288 (1997). https://doi.org/10.1007/s001220050694
  17. Goldschmidt EE, Bar-Joseph M, editors. The Citron Compendium: The Citron (Etrog) Citrus Medica L.: Science and Tradition. Springer Nature; 2023 Jun 7. Chapter 7.8.1, Tristeza; p. 176.
  18. Levy, Y., & Lifshitz, J. (1995). Alemow (Citrus macrophylla Wester.), compared with six other rootstocks for nucellar “Minneola” tangelo (Citrus paradisi Macf. X Citrus reticulata Blanco). Scientia Horticulturae, 61(1-2), 131–137. doi:10.1016/0304-4238(94)00735-x 
  19. Reuther W, Batchelor LD, Webber HJ. The Citrus Industry. Vol. I. History, World Distribution, Botany and Varieties.
  20. https://tropicalfruitforum.com/index.php?topic=48508.0
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