Apology to a Potter Wasp

11 July 2013

Eumenes fraternus
Family Vespidae
Northeast corner of the garage

(The letter's recipient.)
Dear Ms. Eumenes,

I wish to apologize to you for my actions on 10 July 2013, when I thoughtlessly destroyed the two nests you had constructed on my Pachypodium lamerei and then smeared the caterpillars that were inside across the concrete. I should not have done either of those things.

The brood cells; the one on the left is still being filled; the one on the right is full and has been capped.
I did not intend to inconvenience you; I was merely unfamiliar with your brood cells, and on first glance, feared that they were a gall or other pathogenic growth on my plant. And also I was a bit creeped out by the caterpillars, since to me they're a threat, not baby food.

The caterpillars from the cell that had already been filled. She crammed them in there pretty tightly. Proportionally, that's something like you or I filling a Ford Focus, unassisted, through the driver's side window, with paralyzed German shepherds.
I know that the nests represented a significant investment of effort on your part, in the construction of the chambers themselves, the hunting, stinging, transporting, and shoving of the caterpillars, and the egg laid in the closed nest. Further, I acknowledge that no apology can make up for this loss. Nevertheless, I wished to express my sincere regret, and promise that if you should favor my plants for construction in the future, I am now capable of recognizing your brood cells and will do my best not to harm them until your offspring have matured and emerged.

The caterpillars from the cell that was still being filled. Still alive, technically, but they weren't moving at all when this photo was taken.
I have also instructed my husband and dog not to interfere with your subsequent constructions, if any.

Please do not hesitate to contact me if I may be of assistance (mud, location recommendations, caterpillar scouting) to you in the future.

Sincerely,
Mr. Subjunctive

Five More Plants I'm Not Currently Mad At (H through Pn)

As explained in the first of these posts, I'm currently trying to convince myself that despite a pretty catastrophic spring and summer, some of the plants are still doing reasonably well.

Also I'm trying to justify all the new pictures I've taken recently, since sorting through them all and getting them presentable has taken a lot of my time in the last three or four weeks.


1. Haworthia limifolia var. limifolia

Haworthia spp. and I are not always pleased with one another. Watering is often an issue: their need varies depending on the time of year, and although I know this, I have a hard time remembering when it's time to switch from more water to less water. Most of my plants get the same watering year-round, so there's a tendency to try watering the Haworthias that way too. Then I overwater, and they die, and I remember oh yeah, it's [whatever season it is].

Date: September 2012.
Pot size: 3" / 8 cm (along diagonal).
H. limifolia var. limifolia hasn't had as much of a problem with this as some of the others (it's especially been a problem for H. cymbiformis and Haworthia limifolia var. ubomboensis), though, and in fact has managed to make the most dramatic progress of any of them. Here's what it looked like five years ago:

Date: October 2007.
Pot size: 3" / 8 cm (along diagonal).
Part of the reason it does so much better than the average Haworthia in my care is that it gets better light (from shop lights in the basement) than most of them do. Most of the others have been in my office or in the plant room, and I suspect¹ I've misjudged how much light some of those locations actually receive.

Aside from the light and water issues, H. limifolia var. limifolia has been trouble-free: no insects (that I've seen; it was exposed to the ongoing scale infestation, though I've yet to see any scale on the plant), no complaints about temperature or humidity. I feed by splashing with a little bit of fertilizer at the end of a thorough watering. I haven't had a chance to propagate, though I would like to -- they produce plantlets on runners beneath the soil, which can be removed and potted up individually. Unfortunately, mine has yet to produce any plantlets.


2. Leuchtenbergia principis

I actually have two specimens of Leuchtenbergia principis. The first I bought because it was a cool plant, and I had been assured by PATSP readers that I would like it. The second one I bought because it was an 8-inch (20 cm) pot for $5 (the original was a 6-inch / 15 cm for $25), and I couldn't pass up that deal, duplicate plant or no.²

They're not, as you'll see, particularly rapid growers.

The original plant.
Date: September 2012.
Pot size: 6" / 15 cm.
I probably ought to at least look at the roots sometime soon, if not do a soil replacement or move it up to a bigger pot, but I've been holding off because I'm nervous about it. And fall is a bad time to be doing that anyway.

(original)
Date: somewhere between August and November 2009.
Pot size: 6" / 15 cm.
The other plant is in similar shape:

The later-arriving plant.
Date: September 2012.
Pot size: 8" / 20 cm.
In both cases, the plants have splayed outward a bit in the middle, to try to collect more light. They're in a south window, but there are a lot of things (houses, garages, other plants, walls) blocking the light before it reaches the Leuchtenbergias. Perhaps next year they'll get to spend the summer outside.

The later-arriving plant.
Date: December 2010.
Pot size: 8" / 20 cm.
Other than the splaying, they haven't complained about anything. I wind up watering the 6-inch one about every two weeks, though I slow that down some during the winter. The 8-inch plant gets watered about every four weeks, though it's closer to every two weeks in the summer. Fertilization is as described for the Haworthia. Neither Leuchtenbergia has ever given me any other problems.


3. Pachypodium lamerei

Pachypodium lamerei got to spend the summer outside this year, and responded by growing much more and much faster than I thought it was capable of. The down side to this is that it got top-heavy, and as a result, it got knocked over a lot. On occasion, other plants got knocked onto it, too, hence the lopsided appearance of the plant here:

Date: September 2012.
Pot size: 8" / 20 cm? I'm not sure, and I'm too lazy to get up and measure the pot.
And here it is five years and two repottings ago:

Date: October 2007.
Pot size: 4" / 10 cm.
I've definitely had some problems with P. lamerei in the past: mild cases of spider mites, occasional droplets of a dark brown liquid of unknown origin or significance,³ a tendency to defoliate partially in the winter,⁴ the way they're impossible to handle because of all the stabby spines, etc. But on the other hand, it's still alive and growing after five years, it's looking pretty good, and none of the problems have ever gotten out of control or anything.

Indoors, I water it every two weeks, year-round (unless the soil feels wet -- I do still always check the soil first), with light fertilizer splashed on after the watering, as described for the Haworthia. I try to keep the temperature at or above 60F / 16C. I'd love to propagate this, but it's probably just as well that I can't.⁵ Light is my main problem: last year, it sat in a west window with a bit of supplementary artificial light, and seemed to be okay with that. This year, however, it's gotten too tall to fit in that spot, so I have to give it a less-satisfactory location. It might be a good year to try inducing dormancy, but I probably won't: see footnote 4.


4. Philodendron pinnatifidum 'Spicy Dog'

First up, I have to say: Philodendron pinnatifidum 'Spicy Dog' isn't quite what I'd hoped it would be when I bought it. Nothing wrong with how it's turned out, but it's a lot closer to P. bipinnatifidum now than it was when purchased, and we already had a P. bipinnatifidum. The leaves are a lot more deeply lobed, and the stem's lengthened inconveniently. (I have to prop it up against a wall now, which is only going to become more difficult as the plant grows.)

Date: September 2012.
Pot size: 10" / 25 cm.
It's not really visible in the above picture, but if you were looking at the plant from the side, you'd see that the stem has a fairly pronounced "S" shape to it.

Inconvenient though it is, I'm not mad at it right now because it's always grown well and been problem-free. I mean, if it's too big and has a different appearance than what I wanted, it's hard to argue that those things are the fault of the plant.

Date: April 2010.
Pot size: 6" / 15 cm.
The younger leaves were cooler, though.

It's been getting watered about once a month lately (it might be overpotted a bit). For light, it has four separate windows (east, south, south, west), but they're all at least 6 feet (1.8 m) away, and three of the four are heavily obstructed by plants. How it manages to get by on that is something of a mystery to me, but maybe it's highly motivated: perhaps it knows that it's too big to go anywhere else in the house.

It appears not to mind the temperature and humidity here; I can't recall any pests. Propagation is out of the question, for the same reasons as Pachypodium, but there'd be no space for more of them even if I could propagate.


5. Plectranthus verticillatus

Perhaps an odd choice, but I've been appreciating P. verticillatus a lot lately even though it's one of the few plants that's actually decreased in size since I've had it.

Date: September 2012.
Pot size: 4.5" / 11.5 cm.
The original plant made it up to an 8-inch hanging basket --

Date: July 2010.
Pot size: 8" / 20 cm?
-- and then I took cuttings to make a second 8-inch hanging basket. Plus a whole bunch of 4-inch pots I'd propagated from cuttings. The 4-inch pots all grew a little too well, to the point where I couldn't untangle them from one another, and they were always dry, and I realized nobody was going to buy them, so I threw them all out. And then the two hanging baskets both just kind of fell to pieces. I suspect that was a temperature problem, because I'd put them in one of the worst spots imaginable for a tropical plant: near the floor of the room with the least insulation in the house, and directly in the path of a heat vent. So when the heat was on, they got blasted with hot, dry air, and when it wasn't, they were in a cold draft.

Stupid of me, I realize, but it seemed like something they'd be able to handle (they're ordinarily very tough plants), and I didn't have anywhere better to put them. I took cuttings from those before they had completely died, and those salvaged cuttings have turned into two plants, one of which is pictured above.

As to what it's doing on this list, well, they've been living in the basement for a few months now, and the other day I picked them up to water them and I was like, hey, that's actually really pretty, all dark-green and shiny like that. And they're almost too easy to grow, if you're at all trying: mine get water and fertilizer every two weeks, normal household temperatures and humidity (except when they don't), I've never had a pest on any of them, and they're easy to propagate. They're so fast-growing, it can be difficult to keep them under control, so they require some maintenance, but the fast growth is one of the things I liked about the species originally, so I can't really complain about that too much.


Honorable mentions to:

Haworthia NOID (possibly related to H. truncata)
Hoya bella
Hoya lacunosa
Hoya obovata
Huernia schneideriana
Huernia zebrina
Isolatocereus dumortieri
Myrtillocactus geometrizans
Neofinetia falcata Amami Furan
Pandanus veitchii
Peperomia clusiifolia
Peperomia pereskiifolia
Phalaenopsis NOID
Philodendron gloriosum
Philodendron hederaceum 'Aureum'
Pilosocereus pachycladus

As before, this is not an exhaustive list, whatever it might look like: these are just the plants that I happened to take photos of in September and that are still doing well for me.

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¹ (really more like know)
² I've recently been tempted again, because the ex-job got in two or three three-inch (8 cm) pots, and they're so cute that I just about can't stand it --

-- but so far I've been able to resist.
³ Which has happened both indoors and outdoors, and at different times of the year. It also seems to happen mostly near the growing tip, though I've seen it as low as halfway up the stem. It's relatively infrequent: I think I've only seen it four times? There haven't been any signs of bugs, and the last time, this summer, it happened after a particularly bad falling-over, which makes me think it might be related to physical injury, but on other occasions nothing had happened to it before the appearance of the spots, so I'm stumped. I'll try to get a photo the next time it happens.
⁴ The defoliation isn't necessarily a bad thing: they can go dormant if you withhold water, and then come back to life again in the spring. I don't do that because there's no compelling reason for me to do so. That, and I have trust issues about letting plants go dormant, because I always worry that they won't come back again.
⁵ Supposedly they can be propagated from stem cuttings (though I have no idea how in the hell you'd cut one of these stems) or seeds, and there are on-line sources for seeds, but I doubt I could provide enough light to keep seedlings from etiolating, and I don't especially want to cut my plant down, so we'll let it keep doing what it's doing.

Rumble Among the Jungle, Matches 1.5-1.8

Rules and Stuff
1) It's probably possible to vote more than once per poll, but please don't. If I believe that someone is voting repeatedly, I will throw out those results, repost the poll, and seriously question that person's priorities.
2) If you want to link to a poll on Twitter / Facebook / your blog / whatever and encourage your friends to come and pump up the support for your favorite plants, you are encouraged to do so.
3) You are also encouraged to leave comments on Rumble posts, if so moved.
4) All photos will enlarge if opened in a separate window/tab.
5) You can choose which plant is "best" according to whatever criteria you decide for yourself. My personal process is a bit convoluted.¹
6) All polls will be open for three days.

Match 1.5
Saintpaulia cvv. (African violet) vs. Hemigraphis exotica (purple waffle plant)

Saintpaulia cvv.
Top row, L-R: NOID, assorted NOIDs, NOID.
Middle row, L-R: NOID, NOID, NOID.
Bottom row, L-R: 'Harmony's Red Star,' 'Mellow Magic' close-up, NOID.

Hemigraphis exotica, species.





Match 1.6
Cyclamen persicum (florists' cyclamen) vs. Echinopsis spp.

Assorted NOID Cyclamen persicums.

Unidentified Echinopsis sp. Probably.





Match 1.7
Pachypodium spp. (Madagascar palm) vs. Epipremnum aureum cvv. (pothos)

L-R: P. lamerei, close-up of P. lamerei trunk, NOID.

Clockwise from top left: Epipremnum aureum 'Neon,' 'Marble Queen,' 'N'Joy,' trained on a totem.





Match 1.8
Scindapsus pictus (satin pothos) vs. Crassula ovata/argentea/arborescens (jade plants)

(All Scindapsus pictus, possibly different cvv.)

Clockwise from top left: variegated Crassula ovata, C. ovata 'Gollum,' C. arborescens var. undulatifolia, C. ovata.





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¹ I'm deciding according to a hypothetical situation in which all of my houseplants are gone, as are all the other houseplants of the world, except for one producer/supplier/retailer. Said person is offering to restock me with one or the other of the plants in question but refuses to give me both. Which one would I choose?

Random plant event: Pachypodium geayi lamerei

My Pachypodium lamerei (which I've been thinking was a P. geayi for years, but apparently not) has responded well to the fertilizer this spring. It's retained its leaves longer, and put on more vertical growth, than in previous years. The leaf tips still scorch, which I'm thinking is probably a signal that it's too hot or too dry (?), but aside from that, it looks pretty healthy and happy. I noticed on Friday while watering that it's even growing a new side branch (circled above).

I was slightly shocked when I checked the spreadsheets and found out that I've had this plant for a little over four years now. I got it at Wal-Mart in May 2007 for 53 cents, though it was tagged $3.97. Never did figure out what happened there, but it's probably the best plant-related 53 cents I've ever spent.

List: The Best Houseplants You're (Probably) Not Growing

This list isn't intended to be taken very seriously. It's subjective, and even where it's not, we're only talking about my personal experience, over a pretty limited amount of time;¹ the plant might be completely different for you. Having said that, these are the plants that:

1) have performed well for me for a long time,
2) aren't already common in stores (at least not the stores I visit),
3) typically do well indoors for other people too, as far as I know, and
4) have that special something that makes me want to recommend them to everybody.

This is slightly self-interested, as a few of these are plants I will have available for trade or sale at some point,² but it's sort of a chicken-and-egg problem. I have them to sell because I like the plant, and in a lot of cases I like the plant because it's easy to reproduce for selling. The main point of the list is not to promote plants because I'll have them for sale, I swear, it's to say nice things about plants that have been making me happy lately. Because there are a lot of plants that don't.³ (Including some of the plants I want to sell or trade away.)

Agave desmettiana. Fairly rapid growth, as indoor Agaves go, interesting color (on the variegated variety), and so far it doesn't seem especially needy or buggy. If you have full sun and can water thoroughly and regularly, you can grow this.

Eucharis grandiflora. Beautifully fragrant (if short-lived) white daffodil-like flowers up to three times a year, large, glossy green leaves the rest of the time, cold-tolerant, and I've never had problems with bugs. Needs some light (filtered sun or bright indirect), and don't overwater. May go dormant if too dry or dark.

Gasteraloe x beguinii. (Aloe aristata x Gasteria batesiana). Nice form and color, tolerates fairly low light for a succulent, resilient as hell, offsets are easy to root, never a bug problem. Probably won't flower indoors, but it's my favorite foliage Aloe/Gasteria/Haworthia, easily. Give it at least some sun indoors, or else bright artificial light, and don't overwater.

Hatiora salicornioides. Only minor bug problems so far (spider mites, surprisingly), and the flowers aren't the glamour bombs that Eucharis's are, but the form is interesting, and it's easy to grow with full sun to bright indirect light. Fertilizer seems to be more important than I expected: some of mine have only started putting out new growth since I started using the Miracle Gro.

Hoya lacunosa. Easily brought into bloom (it basically just takes lots of light + fertilizer), and can be more or less continuously in bloom year-round. Neither the flowers nor the leaves are much to look at, but it's fairly non-demanding, and the scent is nice.

Pachypodium lamerei. Less easy than most of the other plants on the list -- it's obviously a pain to repot, and it's inclined to winter spider mite infestations and/or dormancy, plus they'll rot if you get them cold and wet at the same time. But they're still fairly easy to grow, and they're tough enough that I've never actually seen one rot from being too wet: I've only heard about it.

Selenicereus chrysocardium. You're probably never going to see the large, overwrought flowers, but with stems like these, who needs flowers? It's fast, it's huge, it's easy to grow (you need only regular watering and a sensible amount of light), I've never had pest problems, and it's just so weird.

Synadenium grantii. I praise Synadenium pretty much every chance I get, but it's difficult to articulate why I like it as much as I do. I like the textures, both visual (red-speckled green, or plum with specks of green) and tactile; I like that they grow fast and can be endlessly duplicated. I love that I've never had a pest problem on a Synadenium. Just a good, vigorous plant for someone with bright indirect light or brighter. They will occasionally drop lower leaves, for reasons I've never been able to figure out but suspect is water-related.

Vriesea splendens. I've always loved the way these look, but it took me a long time to decide to buy one, because all the books warn about them being fussy and difficult. They're not. I've had no pest problems, they seem perfectly happy under artificial light, bright indirect light, or filtered sun, and recently one has even decided to rebloom for me. Occasionally I let them get too dry, and then leaves curl and yellow, but that's been about it for problems.

Zingiber malaysianum. The leaves are pleasantly (if lightly) scented, glossy, and beautiful with light shining through them. It insists on being kept warm (above 50F/10C) and moist, more so than almost any other plant I own (I deal with this by watering every time the watering cycle gets around to it, and if I start finding that it's dry by the time I'm ready to water it, I move it up into a larger pot.), and I suspect that it's probably prone to mites, though I haven't experienced this personally. But I am so pleased with it.

Honorable mentions:

• Aechmea fasciata -- in the trade for a long time, but I rarely see any for sale that aren't already in bloom, and I don't know why. They're perfectly nice foliage plants, and if you buy one already in bloom then it's just going to die on you. (Granted, that can take more than two years, as it did with mine.)
  
• Araucaria bidwillii -- I know why this isn't sold more in the trade. They're kinda ugly, and even the fuller-looking larger specimens are sharp. I love mine anyway.
• Epiphyllum oxypetalum -- The flowers are pretty, but I'm not sure they're actually worth growing the plant for, since they only last for an evening. I like the plant enough that I'm willing to grow it for the unusual, awkward stems, though.
• Euphorbia trigona -- One of my oldest and best-behaved plants, not counting a minor pest problem when I first got it,⁴ plus I like the shape.
• Haworthia limifolia var. limifolia -- I started out liking other Haworthias more, but this one's grown on me. The color (metallic gray or gray-green, depending on culture) is neat, the texture is pleasant, and it may be the only Haworthia species I've had that's never given me trouble.
• Pandanus veitchii -- Of course. Minor pest problems (caterpillars or crickets or something, when I had mine outside last summer), painful to move around, and the tips burn if the plant is in the path of a heat vent, but mostly a piece of cake to grow.
• Polyscias scutellaria -- Polyscias in general have been nice to me, though they do have their moods. P. scutellaria is my favorite of the genus because it's been the most responsive to my care so far (bigger leaves, more leaves), but I also like the look of it.
• Senecio rowleyanus -- We went through some rough times at first, mostly because I wasn't watering enough, but we've reached an agreement since then, and it's grown a lot in the last year. Haven't seen flowers yet on my personal plant, but I look forward to the day: they smell like Big Red chewing gum.

What plant(s) you don't see for sale very often would you add to the list?

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¹ The plants on the list have all been in my care for at least 22 months; the most recent addition (Zingiber malaysianum) was purchased in June 2009, and the oldest (Gasteraloe x beguinii) is from November 2006.
² (I've been having trouble getting suitable photos of the plants in question, among other things. Too bright, too dark, always desaturated: it's frustrating. There's also the issue that some of the plants I had hoped to sell are not looking as good now as I had hoped they would, and it's probably too late to whip them into shape, which is demotivating. I spent the bulk of Wednesday taking pictures, and that set is the set I'm going to use, whether they're good or not. I'm currently planning the official unveiling for April 18, but that may be optimistic, given the number of photos I have to sort through.)
³ [shaking fist at sky:] RADERMACHERA!!!!!!!!!! (Actually, I got rid of the Radermachera a couple weeks ago. I'm still angry, though.)
⁴ It was either whitefly or scale; it happened long enough ago that I don't have any pictures, and don't remember that well. I assumed they were whiteflies, because they flew, but my memory tells me they looked more like immature scale. They went away, whatever they were.

List: Houseplants That Get Tall But Stay Narrow

A very long time ago, someone at Garden Web asked for suggestions for a tall, narrow plant that would stay narrow, rather than spreading out and becoming vase-shaped with time. The reason was because the person had a fairly limited amount of floor space, and wanted the plant in an entryway, so any plants that got wide would eventually take up too much space and no longer be usable in that spot. I provided a number of suggestions in the thread, which for some reason has become a really reliable source of blog hits ever since. Which is kind of weird. I mean, I wouldn't have thought that many people have this problem.

So anyway. Here's a slightly expanded list of more or less upright, narrow, columnar plants that can be kept indoors. They're not all interchangeable -- you'd still need to be able to provide the right conditions as far as light, temperature, etc. And some of them do actually get a little wider with age. But the list below is at least a place to start, when looking for plants that will become tall but not take up a lot of floor space.

Suggestions are welcome, if readers can think of any other plants that fit the category.

Beaucarnea recurvata.

Chamaedorea metallica.

Cordyline glauca, unless cut back.

Dracaena deremensis 'Janet Craig' (shown) and other D. deremensis varieties, unless cut back.

Euphorbia trigona.

Pachypodium lamerei (shown), P. geayi, and other spp., at least for quite a while when younger.

Pilosocereus pachycladus.

Rhapis excelsa.

Sansevieria trifasciata 'Moonglow' (shown), as well as some other S. trifasciata cvv.

Schefflera actinophylla, unless cut back. Some cvv., e.g. 'Renegade,' have more of a tendency to stay columnar than others.
Of these, my favorite three are probably Dracaena deremensis 'Janet Craig,' Euphorbia trigona, and Pachypodium lamerei.

Dracaena will generally be quite a bit wider than its pot, but it will tend to maintain that width for its entire life, getting maybe a little bit wider at the top with age. If cut back, they will resprout from multiple spots on the stem, making the plant a bit wider, but this takes a very long time to happen and isn't likely to be that big of a deal. They're very tolerant of low light, dry air, and other indoor conditions, but need occasional flushing of the soil with water, because they're somewhat mineral sensitive. They're also easily overwatered, so be sure to only water when the soil is very dry, and when you do water, water thoroughly. Too large of a pot can also cause them problems.

Euphorbia trigona is probably my favorite of the three: it needs very bright light and is easily overwatered, but it is otherwise very easy. As plants age, they will grow new shoots at the stems' corners, which will grow up as well, forming a tall narrow column of stems which is widest in the middle. They will generally need only as much floor space as the pot they're in. The sap is toxic, and may be dangerous to children or pets.

Pachypodium lamerei is of about average difficulty. Like the other two, it's easily overwatered, especially if injured. It needs very bright light and may go dormant during the winter, dropping its leaves and slowing water consumption (this isn't inevitable; my personal plant has never gone completely dormant, as far as I can tell, in the three winters I've had it). It's also more prone to spider mites than the other two, especially during the winter. Very old plants, or plants in very ideal conditions, will branch at the top, though this is not common in plants grown indoors year-round. Pachypodium is also both poisonous and covered in sharp, potentially harmful, spines.

I don't recommend against any of these plants especially, though I personally do poorly with Sansevieria trifasciata and don't intend to buy any more of them for that reason. I think most people have more trouble with Rhapis excelsa.

Not pictured:

Browningia hertlingiana
Carnegiea gigantea
Cereus peruvianus
Cordyline fruticosa, unless cut back
Dizygotheca elegantissima, unless cut back
Dracaena fragrans 'Massangeana,' unless cut back
Dracaena marginata, some specimens, unless cut back
Dracaena reflexa 'Anita,' unless cut back
Dracaena reflexa 'Riki,' unless cut back -- is pretty wide to begin with, but doesn't get a lot wider
Dracaena sanderiana
Euphorbia ammak, kinda (they will eventually branch on their own)
Euphorbia drupifera, kinda (they tend to lean with age, has been my experience)
Euphorbia grandicornis, more or less
Isolatocereus dumortieri
Myrtillocactus geometrizans
Pachycereus marginatus
Polyscias balfouriana
Polyscias fruticosa
Schefflera arboricola, some specimens, unless cut back
Stenocereus pruinosus
Stenocereus thurberi
Yucca guatemalensis, unless cut back

List: Houseplants Which are Highly Prone to Spider Mites

There's no official or definitive list for this; spider mite susceptibility isn't something I've ever tried to quantify. That said, though, there are definitely some plants which are more likely to have mites when you buy them, or more likely to develop a raging case of mites once you get them home.

Thick-leaved succulent plants and cacti tend not to have mite problems; spider mites don't seem to be able to pierce their thicker, waxier epidermises. Consequently, the plants most susceptible to mite attack have broad, thin leaves (like Musa or Dieffenbachia) instead of small, fleshy ones (like Crassula or Hoya). Certain families are apparently also a lot tastier than others; the Araliaceae, Marantaceae, and Apocynaceae seem to be particularly delicious.

(I realize that it would probably be a lot more useful to the reader to present a list of plants which are highly resistant to spider mites, as opposed to plants highly susceptible to them, but that's actually much tougher to do. Even if I've never seen a bad mite infestation on, say, an Aglaonema, I can't really be certain that they're that resistant. Maybe the Aglaonemas with whom I've personally been acquainted have just been really lucky, you know?)

Alocasia 'Frydek.' (also other Alocasia spp.)

Aspidistra elatior 'Milky Way.' (cast-iron plant)

Calathea roseo-picta, possibly cv. 'Rosy.' (also other Calathea spp.)

Chamaedorea elegans. (parlor palm)

Codiaeum variegatum 'Petra.' (croton) (also other Codiaeum variegatum cvv.)

Cordyline fruticosa 'Kiwi.' (ti plant) (also other Cordyline fruticosa cvv.)

Assorted Hedera helix (English ivy) cultivars.

Pachypodium lamerei (Madagascar palm).

Schefflera actinophylla (umbrella tree).

Strelitzia nicolai. (white bird of paradise)

Severity of infestations vary, enough that I really adore some of the above, and refuse to let others in my home. I consider Cordyline fruticosa worth the trouble, and both Pachypodium and Strelitzia are welcome, because they tend not to get out of control mite populations as rapidly as others on the list. Codiaeum variegatum, on the other hand, is a definite planta non grata here, mostly (though not entirely) because of its attractiveness to mites, as are Hedera helix, Calathea spp., and Alocasia spp. All four of those gave us ongoing, substantial problems where I used to work, to the point where I stopped bringing them in. (They've started ordering them again since I left, though, with predictable results.)

Am I missing anything? Let me know in the comments.

Not pictured:
Acorus spp. (sweet flag, Japanese rush)
Adenium obesum (desert rose)
Alternanthera spp. (including A. dentata 'Purple Knight')
Aspidistra elatior (cast-iron plant)
Breynia disticha cvv. (snow bush, snow on the mountain)
Brugmansia cvv. (angel's trumpet)
Chamaedorea seifrizii (bamboo palm)
Cissus rhombifolia (grape ivy)
Colocasia cvv. (elephant ears)
Datura cvv. (devil's trumpet)
Dieffenbachia spp. (dumb cane)
Dracaena marginata (Madagascar dragon tree)
Dracaena thalioides
Gardenia jasminoides (gardenia)
Hedera canariensis (Algerian ivy)
Heliconia psittacorum cvv.
Hibiscus rosa-sinensis (tropical hibiscus)
Impatiens spp. (impatiens)
Jasminum sambac (jasmine)
Maranta leuconeura cvv. (prayer plant, rabbit tracks)
Musa spp. / Ensete spp. (ornamental banana)
Plumeria cvv. (frangipani)
Polyscias balfouriana (balfour aralia)
Polyscias fruticosa (ming aralia)
Primula vulgaris (primrose)
Ravenea rivularis (majesty palm)
Schefflera arboricola (umbrella tree)
Schefflera elegantissima (also known as Dizygotheca elegantissima) (false aralia)
Stromanthe sanguinea cvv.